Geo log i cal Quar terly, 2021, 65: 43 DOI: http://dx.doi.org/10.7306/gq.1612
Epi ther mal Cu min er al iza tion in the Stary Lesieniec rhyodacite quarry, Lower Silesia: pri mary and sec ond ary min eral paragenesis
S³awomir MEDERSKI1, *, £ukasz KRUSZEWSKI2 and Jaroslav PRŠEK1
1 AGH Uni ver sity of Sci ence and Tech nol ogy, al. A. Mickiewicza 30, 30-059 Kraków, Po land
2 Pol ish Acad emy of Sci ences, In sti tute of Geo log i cal Sci ences, Twarda 51/55, 00-818 Warszawa, Po land
Mederski, S., Kruszewski, £., Pršek, J., 2021. Epi ther mal Cu min er al iza tion in the Stary Lesieniec rhyodacite quarry, Lower Silesia: pri mary and sec ond ary min eral paragenesis. Geo log i cal Quar terly, 2021, 65: 43, doi: 10.7306/gq.1612
As so ci ate Ed i tor: Stanis³aw Z. Mikulski
Pri mary epi ther mal and sec ond ary Cu min er al iza tion in the Stary Lesieniec rhyodacite quarry, lo cated within the Intra-Sudetic De pres sion, was stud ied us ing re flected light mi cros copy, pow der X-ray dif frac tion, and elec tron microprobe.
Sam ples con tain ing cop per sulphides, baryte, and sec ond ary weath er ing min er als were col lected from min er al ized veinlets in the Up per Car bon if er ous rhyodacite. Cop per sulphides (chalcocite Cu2S, djurleite Cu31S16, anilite Cu7S4 /digenite Cu9S5, and covel lite CuS) are the ma jor ore min er als and are as so ci ated with quartz, he ma tite, and very mi nor uraninite. The sam - ples stud ied in di cate phase trans for ma tion from chalcocite to anilite, which in di cates that Cu sulphides be gan to crys tal lize at
~100°C. Then, dur ing the epi ther mal stage of pre cip i ta tion, the tem per a ture of the so lu tions dropped <72°C, based on the Cu-S ter nary di a gram and anilite sta bil ity. Ad mix tures of Ag, Fe, Bi, and Se in the sulphides are very mi nor. Supergene paragenesis is rep re sented by chrysocolla with mi nor brochantite and very scarce mal a chite. These only bear trace im pu ri - ties at the an ionic sites. The supergene ox i da tion pro cess be gan with the for ma tion of abun dant chrysocolla, at a rel a tively neu tral pH. Af ter drop ping of the pH to ~4–6, brochantite was de pos ited.
Key words: Stary Lesieniec, cop per sulphides, epi ther mal ore de posit, sec ond ary min er als.
INTRODUCTION
Cop per sulphides of the Cu-S sys tem are the most com mon cop per-bear ing phases in many dif fer ent ge netic types of cop - per ore de pos its, and are among the most im por tant cop - per-bear ing phases in the min ing in dus try. They may form dur - ing pri mary-hy dro ther mal or sec ond ary-weath er ing pro cesses, usu ally at low or me dium tem per a tures (e.g., Sillitoe and Clark, 1969; Hatert, 2005; Mathur et al., 2018). Pri mary chalcocite may crys tal lize as three main ge netic types, un der the fol low ing con di tions: hypogene hy dro ther mal de pos its (>150°C), red bed or stratiform de pos its with cir cu lat ing flu ids through sed i men - tary bas ins (<150°C), or supergene en rich ment ores that pre - cip i tate from low- to am bi ent-tem per a ture ox i da tive flu ids in near-sur face en vi ron ments (Mathur et al., 2018). The most com mon en vi ron ment here is the ce men ta tion part of the supergene en rich ment zone of var i ous cop per de pos its – por - phyry, SHMS (sed i ment-hosted mas sive sulphides), VHMS (vol ca nic-hosted mas sive sulphides), stratiform or hy dro ther -
mal types (Sillitoe and Clark, 1969; Gablina et al., 2006; Belo - gub et al., 2008; Mathur et al., 2018).
Min er als of the Cu-S sys tem have a nar row field of sta bil ity in low-tem per a ture con di tions and they eas ily trans form to each other dur ing var i ous nat u ral pro cesses (Goble, 1980; Goble and Rob in son, 1981; Pósfai and Buseck, 1994). Usu ally, the for ma tion of these Cu-sulphides starts with the crys tal li za tion of chalcocite and ends with covel lite, at low tem per a tures. An ex - per i men tal study pro duc ing trans for ma tion phase di a grams was de scribed by Roseboom (1966) and fol lowed up by Mori - moto and Koto (1970), Cook (1972), Pot ter (1977), Ev ans (1981), to gether with equi lib rium in ves ti ga tions by Schmidt et al. (1998).
Cu sul phide de pos its in Po land are known within the Pol ish Kupferschiefer, where the min er als of Cu-S sys tem are pri - mary (mainly chalcocite, djurleite, more rarely covel lite) or sec - ond ary (dige nite, covel lite) (Saw³owicz, 1990; Large et al., 1995; Pieczonka et al., 2007; Wodzicki and Piestrzyñ ski, 2014; Mikulski et al., 2020; Szopa et al., 2021). They are also known from Miedzianka near Chêciny (Holy Cross Mts., cen - tral Po land), Miedzianka-Ciechanowice (Rudawy Janowickie Moun tains, Sude tes, Lower Silesia), and from the Radzimo - wice de pos its (Zimnoch, 1978; Wieser and ¯abiñski, 1986;
Pieczka et al., 1988; Mikulski, 2005; Mochnacka et al., 2012).
Cop per min er al iza tion within vol ca nic rocks is not so com mon in Po land. Ex am ples in clude na tive cop per with cu prite and sec ond ary weath er ing cop per min er als at Soko³owiec (Siwe -
* Corresponding author, e-mail: mederski@agh.edu.pl
Received: May 25, 2021; accepted: August 9, 2021; first published online: September 14, 2021
cki, 2017), na tive cop per in the Rudno and Nowy Koœció³ ag - ates (Krawczyñski, 1995; Dumañska-S³owik et al., 2008), chal co py rite, chalcocite, covel lite, and sec ond ary weath er ing cop per min er als at Zalas (Go³êbio wska et al., 2006), and chal - co py rite and chalcocite at Borówno (Powolny et al., 2019). In ad di tion, Cu min er al iza tion hosted in baryte veins was de - scribed in Zagórze Œl¹skie, where chal co py rite is as so ci ated with sec ond ary mal a chite (Piestrzyñ ski and Kowalik, 2015) and at Przygórze, near Nowa Ruda, where Cu ore com pris ing sim ple Cu sulphides (chalcocite, with mi nor chal co py rite and pos si ble geerite and roxbyite) dis sem i nated in (car bon - ate-bear ing) bary te veins is weath ered, ex clu sively, to slightly magnesian mal a chite, Cu2(CO3)(OH)2 (Kru sze wski et al., 2019). Sim i lar hy dro ther mal cop per min er al iza tion (with chal - co py rite, bor nite, na tive cop per, chalcocite, and other cop per sulphides) has been de scribed from var i ous lo cal i ties world - wide and is mostly con nected with vol ca nic rocks (Rojkoviè, 1990; Rojko viè et al., 1993; Ferenc and Rojkoviè, 2001; Emetz et al., 2006; Cabral and Beaduoin, 2007; Konari et al., 2013;
Németh et al., 2017; Vlasáè et al., 2018; Kettanah, 2019;
Palyanova et al., 2020; and oth ers).
Among the cur rently (May 2021) 5704 ap proved min eral spe cies, there are a great abun dance of sec ond ary weath er ing cop per min er als. Formed due to weath er ing of the pri mary min - er als, the fi nal chem i cal com po si tion, and min er al og i cal com - plex ity of their as sem blages is de pend ent on the in ter ac tion of the weath er ing prod ucts with el e ments and ions con tained in both the coun try rock and so lu tions de rived, e.g., from me te oric wa ters. The most com mon de pos its with a broad range of sec - ond ary cop per min er als are the Miedzianka and Radzimowice lo cal i ties (Wieser and ¯abiñski, 1986; Pieczka et al., 1988;
Siuda and Kruszewski, 2006, 2013; Siuda and Go³êbiowska, 2011; Swêd et al., 2015; Parafinuk et al., 2016).
This study de scribes the min er al ogy and phase tran si tions in low-tem per a ture epi ther mal cop per-baryte min er al iza tion with sec ond ary phases iden ti fied in a rhyodacite quarry at Stary Lesieniec. Both pri mary and sec ond ary min er al ogy is ad - dressed here.
LOCALITY AND GEOLOGICAL SETTING
The Stary Lesieniec rhyodacite quarry is lo cated within the ad min is tra tive bound aries of the west ern part of the town of Boguszów Gorce, ~8 km west of Wa³brzych and ~1 km south- west of Mniszek Hill. The quarry is sit u ated within the Wa³brzych De pres sion, which is part of the Intra-Sudetic Ba sin (ISB). The 70 km long and 35 km wide ISB is lo cated at the NE mar gin of the Bo he mian Mas sif (Holub, 1976; Lorenz and Nicholls, 1976;
Wojewoda and Mastalerz, 1989; Awdankiewicz et al., 2003).
The struc ture is filled with a lower Car bon if er ous to up per Perm - ian molasse suc ces sion, com pris ing var i ous Car bon if er ous and Perm ian volcanogenic rocks with com mon inter beds of sed i - men tary and tuffogenous de pos its. Volcano genic rocks are linked to a post-collisional ex ten sion-re lated set ting in tran si tion to a within-plate set ting (Awdankiewicz, 1998, 1999; Mikulski and Wil liams, 2014) and re sult from sub se quent Early Perm ian mag matic ac tiv ity (Koz³owski, 1958, 1963).
The rhyodacites form a sheet-like, con form able body, up to 200 m thick in the east ern-cen tral part, and wedge out west- and south wards (Fig. 1). The vol ca nic body is un der lain by the top most de pos its of the Žácleø For ma tion (Westphalian B/C) and is over lain by the Ludwikowice For ma tion (Up per Ste pha - nian). In ad di tion, the SE part of the rhyodacites oc curs within the Glinik For ma tion (Westphalian/Stephanian). Ac cord ing to Awdankiewicz (1999), the rhyodacites are most prob a bly of ex - tru sive or i gin (Grocholski, 1965; Nemec, 1979). The rhyodacite, which is phenocryst-rich, is char ac ter ized by the pres ence of co lum nar joints per pen dic u lar to the mar gins of the rock body (Awdankiewicz, 1999). Some of these co lum nar joints, oc cur - ring within the west ern wall of the quarry, are filled with epi ther - mal Cu min er al iza tion, which is the sub ject of this study.
MATERIALS AND METHODS
Sam ples of min er al ized rocks were col lected from the west - ern part of the quarry (50°45’17" N, 16°10’17" E). The sam ples
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Fig. 1. Sim pli fied geo log i cal map of the Stary Lesieniec area
SLRd – Stary Lesieniec rhyodacites, ChRd – Che³miec rhodacites, MRdPh – Mniszek rhyodacite phacolith (mod i fied from Grocholski, 1973; Awdankiewicz, 1999)
were care fully checked mac ro scop i cally and se lected for fur ther mi cro scopic and Pow der X-Ray Dif frac tion (PXRD) stud ies, as well as microprobe anal y sis.
The sam ples were ground in ag ate mor tar and ana lysed us - ing PXRD method for phase and struc tural anal y sis. A Bruker axs D8 ADVANCE diffractometer, equipped with VNTEC-1 superfast lin ear po si tion-sen si tive de tec tor (LPSD), CoKa ra di - a tion source (kb-fil tered), with no mono chro ma tor, was used.
An in cre ment of 0.02 2q was used with 1s/step (~416 s/step in the LPSD lan guage), and the sam ples were ex posed in the 3–80 2q range. For the struc tural anal y sis (i.e., unit cell pa ram e - ters cal cu la tion), the PXRD data were mod elled us ing the Rietveld re fine ment method (Rietveld, 1967) im ple mented in TOPAS v. 4.0 soft ware. In quan ti ta tive phase anal y sis (QPA) of the sam ple, in the case of chrysocolla (lack ing struc tural model), the in put data were in tro duced as a hkl phase (Pawley method, Pawley, 1980). The re fine ment pro ce dure was con - trolled, i.e., by the at ten dance of one of us (£.K.) in the Reynolds Cup 2018 com pe ti tion. De tails of the re fine ment ap - proach are de scribed in Kruszewski (2013).
The chem i cal com po si tion of the pri mary min er als was stud ied by EPMA, us ing the JEOL Super Probe 8230 in the Lab o ra tory of Crit i cal El e ments at the Fac ulty of Ge ol ogy, Geo - phys ics and En vi ron men tal Pro tec tion, AGH-UST, Kraków.
The fol low ing op er at ing con di tions and stan dards were used:
ac cel er at ing volt age 20 kV, beam cur rent 20 nA, and a beam di - am e ter of 5 µm. The fol low ing wave lengths (to omit in ter fer - ences be tween the el e ments’ spec tral lines) were used: ZnKa, CuKa, SKa, FeKa, AgLa, AsLa, SbLa, BiMa, SeLa. Nat u ral min eral stan dards (FeS2, ZnS, PbS) and syn thetic com pounds (Sb2S3, Cu, Ag, Bi, Se) were used for cal i bra tion. All in ter fer - ences be tween the el e ment spec tral lines were cal cu lated us ing autocorrections based on stan dards. The de tec tion lim its for el e - ments anal y ses in the Cu sulphides were as fol lows: S – 0.01 wt.%, Cu – 0.025 wt.%, As – 0.03 wt.%, Sb – 0.02 wt.%, Bi – 0.05 wt.%, Ag – 0.02 wt.%, Zn – 0.03 wt.%, Fe – 0.01 wt.%, Se – 0.075 wt.%.
The chem i cal com po si tion of the sec ond ary min er als was also stud ied by EPMA, us ing a Cameca SX100 microprobe lo - cated in the Inter-In sti tu tion Lab o ra tory of Microanalysis of Min - er als and Syn thetic Sub stances, In sti tute of Geo chem is try, Min er al ogy and Pe trol ogy, Fac ulty of Ge ol ogy, Uni ver sity of War saw. A stan dard 15 keV cur rent was used. Two other cur - rent pa ram e ters – am per age and beam size – and their in flu - ence on the wt.% val ues were tested be fore es tab lish ing the fi -
nal ones: 5 nA and 10 mm for chrysocolla (and sim i lar sil i cates);
10 nA and 5 mm for brochantite and mal a chite. The fol low ing stan dards were used: di op side (Si, Mg, Ca), orthoclase (Al, K), cu prite (Cu), sphalerite (Zn), Fe2O3 (Fe), rhodo nite (Mn), baryte (S), tugtupite (Cl), rutile (Ti), YPO4 (P), and V2O5 (V). Due to pos si ble in ter fer ences, Na pres ence and line co in ci dence was tested via WDS scan ning; Na pres ence was not con firmed in the min er als stud ied. The re ported wt.% are not nor mal ized, as will be ex plained be low.
RESULTS
Sam ples of the min er al ized veinlets were taken from the west ern walls of the quarry, at the lower min ing level (Fig. 2).
This min er al iza tion filled co lum nar joints, the pa ram e ters of which are as fol lows: dip di rec tion: 56–83°, dip an gle: 60–77°.
PRIMARY MINERALS
Cop per sulphides (chalcocite Cu2S, djurleite Cu31S16, anilite Cu7S4/digenite Cu9S5, and covel lite CuS) are the ma jor ore min - er als and are as so ci ated with baryte, quartz, and sec ond ary min er als in small veinlets (up to 10 cm width). The best QPA model for the ore sam ple is ob tained when low-tem per a ture, trigonal digenite is in cluded. How ever, the re sults are very sim i - lar to those ob tained in a digenite-free model. The ore com po si - tion is (in wt.%): 69.6(7) low-tem per a ture chalcocite, 7.3(7) anilite, 6.23(8) djurleite, and 0.223(7) digenite, with the re main - der of 16.8(5) be ing baryte (Rwp = 8.46%, GOF = 1.63%, DW = 0.78%, where: Rwp is the re sid ual weighted-pat tern, GOF is good ness of fit also known as c2, and DW is Durbin-Wat son sta - tis tics). Min er als re lated to sul phide paragenesis dif fer in Cu/S ra tio (Fig. 3) and do not show sig nif i cant en rich ment in the trace el e ments (TEs) mea sured. The con tent of in di vid ual TEs is not de pend ent on sul phide spe cies sys tem at ics. The Ag con cen tra - tion in the sulphides reaches up to 0.18 wt.%; Bi – up to 0.16 wt.%; Se – up to 0.19 wt.%; and Fe – up to 0.03 wt.% re - spec tively.
Chalcocite is the dom i nant min eral phase in sul phide inter - growths and forms ag gre gates up to few centi metres in di am e - ter (Fig. 4A–D). It is char ac ter ized by a blue-grey col our and weak ani so tropy. The gen er al ized chalcocite for mula based on
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Fig. 2. Field im ages from the Stary Lesieniec rhyodacite quarry
1 an ion is Cu1.96–2.00S1.00 (Ap pen dix 1*, anal y ses 1–8). The Cu/S ra tio is 1.96–2.00 (Fig. 3). Most of the val ues are very close to the ideal Cu/S ones (2.00). The unit cell pa ram e ters of the chalcocite are: a = 15.279(1), b = 11.77(1), c = 13.488(9), and b = 116.85(5)o.
In the sam ples stud ied, djurleite is less prev a lent. It shows weak ani so tropy, a blu ish-grey col our, and a lower reflectance as com pared to the chalcocite. It usu ally forms ir reg u lar inter - growths in chalcocite ag gre gates (Fig. 4C, D). Djurleite is ei ther syn chro nous with or youn ger than the chalcocite. The gen er al - ized em pir i cal djurleite for mula based on 16 an ions is:
(Cu30.46–31.38Ag0.01–0.03Bi0.00–0.02Fe0.00–0.01)S30.51–31.42(S15.95–16.00Se
0.00–0.05)S16.00 (Ap pen dix 1, anal y ses 9–14), while the Cu/S ra tio is 1.93–1.96 (Fig. 3). A lot of the Cu/S val ues are very close to the ideal ones (1.94). The PXRD pat tern of the djurleite was in - dexed on a monoclinic unit-cell, with a = 28.65(9), b = 15.637(6), c = 13.43(4), and b = 89.23(25)o.
Anilite/digenite forms elon gated lamellae, up to 1 mm long, along the cleav age planes in older Cu sulphides (Fig. 4A, C, D). It is more com monly found within chalcocite crys tals (Fig.
4A, C) than in djurleite (Fig. 4D). Anilite/digenite are char ac ter - ized by a dis tinctly light blue col our and sig nif i cantly lower reflectance than the pre vi ously men tioned sulphides. The gen - er al ized for mula based on 5 an ions can be ex pressed as (Cu9.01–9.40Ag0.01)S9.02–9.42(S4.99–5.00Se0.00–0.01)S5.00 (Ap pen dix 1, anal y ses 15–18). The Cu/S ra tio is 1.81–1.88 (Fig. 3), which sug gests a chem i cal com po si tion closer to digenite. On the other hand, the amount of anilite out weighs the amount of digenite, as shown by QPA. The con tent of the par tic u lar spe - cies is thus likely very vari able among the min er al ized zone.
The unit cell pa ram e ters of anilite are a = 7.928(7), b = 7.78(3), and c = 10.97(1); those of digenite are as fol lows: a
= 16.50(5), c = 14.28(19).
Frac tures cross-cut ting older sul phide masses and con tacts be tween chalcocite and djurleite are of ten filled with sec ond ary covel lite (Fig. 4D). This is char ac ter ized by the typ i cal in - digo-blue col our, strong bireflectance, and strong, pink ish to or - ange, ani so tropy. It should be men tioned that within the veinlets there are non-cracked, fresh sul phide zones, and zones with a higher pro por tion of brecciation bear ing covellites and other
sec ond ary phases. The gen er al ized covel lite for mula based on 1 an ion is Cu1.04–1.07S1.00 (Ap pen dix 1, anal y ses 19, 20). The Cu/S ra tio in covel lite var ies from 1.04 to 1.07, which in di cates a higher cop per con tent and tran si tional chem i cal char ac ter, be - ing in ter me di ate be tween covel lite and yarrowite (Fig. 3).
Baryte form ir reg u lar masses as well as idiomorphic crys - tals up to 2 mm long be tween chrysocolla and rhyodacite clasts (Fig. 4E). The voids within the baryte are usu ally filled with chrysocolla. Fi nally, the pa ram e ters of the baryte are a = 8.866(4), b = 5.447(3), and c = 7.148(3). The re lated sta tis - ti cal pa ram e ters are: Rwp = 7.69%, GOF = 1.55%, DW = 0.87%.
The baryte crys tals are char ac ter ized by the pres ence of nu - mer ous fluid in clu sions, as well as fi brous he ma tite ag gre gates (Fig. 4F).
Quartz oc curs as idiomorphic crys tals with di am e ters up to 100 mm, which in ter sects Cu sul phide ag gre gates as well as baryte crys tals.
As many as 3 larger in clu sions of an U-O phase were de - tected within a sin gle microarea of chrysocolla (Fig. 5D). In ad - di tion, one larger crys tal was ob served in a chalcocite ag gre - gate (Fig. 4B). Only two anal y ses were pos si ble, with the fol - low ing wt.% con tents: P2O5: 0.00, 0.45; SiO2: 2.62, 6.46; UO2: 84.27, 77.39; Al2O3: 0.09, 0.57; CuO: 5.90, 4.64; PbO: 1.43, 0.00; MnO: 0.00, 0.66; CaO: 3.17, 4.06; K2O: 0.00, 0.24; with to tals of 97.48 and 94.47, re spec tively, and S, Th, Zr, Ti, Fe, and Mg ox ides were be low their de tec tion lim its. Af ter de duc - ing the largely vari able Si con tents, and also Cu and Al con - tents as in ter fer ences from the ma trix, the anal y ses recasted with a 4-cat ion ba sis give the mean for mula of (U4+0.80Ca0.18Mn0.01Pb0.01)S1.00O1.80. The low ered cal cu lated O amount sug gests the min eral to be the “pitch blende” va ri ety, U3O8. A re-recasted anal y sis, based on the sug gested av er - age U va lency of 5.775 (Estep, 2012), gives the for mula (U2.40Ca0.53Mn0.04Pb0.03P0.01)S1.00O7.56.
SECONDARY MINERALS
Chrysocolla, Cu2-xAlx(H2-xSi2O5)(OH)4 · nH2O (x <1), and/or its amor phous pre cur sor is the ma jor sec ond ary Cu spe cies in
4 S³awomir Mederski et al. / Geological Quarterly, 2021, 65: 43
Fig. 3. Chem i cal com po si tion of cop per sulphides from the Stary Lesieniec rhyodacite quarry
* Supplementary data associated with this article can be found, in the online version, at doi: 10.7306/gq.1612
the ma te rial stud ied. Most chrysocolla ag gre gates are mas sive and vivid blue, with some sharp out lines of a crys tal line pre de - ces sor ob served only lo cally (Fig. 5A, C, D). The blu ish-white va ri ety of chrysocolla is rare. The chrysocolla is lo cally cov ered by very tiny (<1 mm long) bright green, cha ot i cally intergrown nee dles of brochantite, Cu4(SO4)(OH)6 (Fig. 5B). Its typ i cal, high-lus tre, flat lamellar crys tals are also ob served lo cally, cov - er ing the baryte (Fig. 5E), but this type of habit is rare. Mal a - chite, Cu2(CO3)(OH)2 was only de tected in tiny amounts in a sin gle sam ple, cov er ing the baryte. It is dif fi cult to mac ro scop i - cally dis tin guish from brochantite due to its tiny size. The iden - tity of black specks of a mas sive sub stance very lo cally cov er - ing the chrysocolla could not be de ter mined via the PXRD, pre - sum ably both to their low vol ume and low crystallinity. How ever, black, typ i cally den dritic “wad”, cov er ing rocks in the outer part
of the ex po sure was shown by hand-held X-Ray Flu o res cence Spec tro scope (pXRF) to be, in deed, a Mn-(hydr)ox ide, bear ing es sen tial ad mix tures of Cu, Ni, and Co. Va na dium was of ten seen in some pXRF spec tra but this find is not well-founded in the EPMA study which did not al low de tec tion of this el e ment in any of the pri mary and sec ond ary min er als ana lysed. It is thus sus pected that V oc curs in the rock ma trix.
Only a sin gle sam ple stud ied by PXRD has shown a few re - flec tions at trib ut able to chrysocolla, at d = 1.467 (very broad) 2.876 and 4.421 (both broad), with the one at 17.16 be ing very dif fuse and low in its in ten sity. The cal cu lated unit cell pa - ram e ters are: a = 5.799(6), b = 17.64(1), c = 8.081(7) (Rwp
= 4.72%, GOF = 1.42%, DW = 1.02%). Pa ram e ters ob tained for brochantite are a = 13.096(6), b = 9.868(4), c = 6.022(2), and b = 102.93(7)o (Rwp = 9.18%, GOF = 1.54%, DW = 0.90) for
S³awomir Mederski et al. / Geological Quarterly, 2021, 65: 43 5
Fig. 4. Back-Scat tered-Elec tron (BSE) im ages (A, B), op ti cal [re flected light, 1P (C, D);
2P (E, F)] il lus trat ing the pri mary as sem blage from Stary Lesieniec
A – chalcocite (cc) with elon gated anilite/digenite (an/dg) lamellae along the cleav age planes sur - rounded by youn ger baryte (ba); B – idiomorphic uraninite (ur) crys tal in chalcocite; chrysocolla (ch); C – chalcocite with ir reg u lar djurleite (dj) zones and youn ger elon gated anilite/digenite lamellae; D – dis in te grated chalcocite–djurleite–anilite/digenite ag gre gates with sec ond ary covel - lite (cov) veinlets; E – idiomorphic baryte crys tals be tween rhyodacite (rh) clasts sur rounded by chrysocolla (ch); F – fi brous he ma tite (hem) crys tals in baryte
one sam ple; and a = 13.153(7), b = 8.890(6), c = 5.987(3), b = 104.13(7)o (Rwp = 17.78%, GOF = 2.64%, DW = 0.32) for the sec ond sam ple. Pa ram e ters ob tained for mal a chite are: a = 9.485(4), b = 11.955(4), c = 3.2443(9), b = 98.69(2)o (Rwp = 14.49%, GOF = 1.82%, DW = 0.63). The unit cell pa ram e ters of brochantite from the two sam ples stud ied are sim i lar to each other, and vari a tions are as low as 0.44 for a, 11 for b, 0.58 for c, and 1.2% for b. Larger dis crep an cies be tween the two cal cu - lated b pa ram e ters may be ex plained by a larger de gree of free - dom in the unit cell pa ram e ters vari a tions due to the low (monoclinic) sym me try of brochantite. On the other hand, the qual ity of the sec ond-sam ple re fine ment is lower and thus of
lower re li abil ity. Typ i cal pub lished unit cell pa ram e ters of brochantite are a = 13.08, b = 9.85, c = 6.02 and b = 103.37o (An thony et al., 2003) and, thus, the dif fer ence is 0.12, 0.18, 0.03, and 0.44%, re spec tively, when com pared with our data for the first sam ple. Due to the pure chem i cal na ture of the brochantite stud ied (as ex plained be low) the sim i lar ity of the val ues to these pub lished ones are clear.
The sec ond ary min er als stud ied are, in gen eral, very pure chem i cally. The chem is try of chrysocolla is quite vari able in terms of the pro por tions of its con stit u ents, but not in terms of their chem i cal type.
6 S³awomir Mederski et al. / Geological Quarterly, 2021, 65: 43
Fig. 5. Full-col our (A, B) and Back-Scat tered-Elec tron (BSE, C–F) pho to mi cro graphs of the sec ond ary as sem blage from Stary Lesieniec
A – pseudomorphous bright blue chrysocolla (ch) in the baryte-rich ma trix (ba); B – bright green sprays of brochantite (bc) nee dles among colour less baryte; C – BSE-bright baryte (ba) sur - rounded by chrysocolla/quartz (ch/q) and a Cu-Mg-Fe alu mi no sili cate (cmf); D – chryso - colla-dom i nated ma trix with BSE-brighter veinlets of baryte and quartz, and tiny BSE-bright est in clu sions of uraninite [and mi nor zir con and/or monazite-(Ce)]; E – large rounded ag gre gate of brochantite with in clu sions of rem nant Cu sulphides (cs), within chrysocolla/quartz ma trix cut by baryte veinlets; F – tiny BSE-dark in clu sion of ei ther a Fe(Cu) alu mi no sili cate (in the mid dle) or he ma tite among chrysocolla
Sam ple BK1. Ex am ples of chrysocolla anal y ses are shown in Ap pen dix 2 (anal y ses 1–5). SiO2 var ies in the 43.13–45.74 wt.% range and the cor re spond ing ranges for Al2O3, CuO and CaO are 1.88–2.00, 45.73–46.90, and 0.87–1.10, re spec tively. The anal y ses re cast to (Cu1.69Al0.11Ca0.05)S2.00[H0.12Si2.32O5](OH)3.50 · nH2O (Cu + Al + Ca = 2 ba sis). Re cast ing these anal y ses to 4 at oms gives the for mula (Cu1.71Al0.11Ca0.04)S1.85[H0.11Si2.15O5](OH)2.41 · nH2O.
Some fur ther Cu sil i cate spe cies were de tected in the sam ple BK1-1 (Ap pen dix 3, anal y ses 1–7). These are dis - sem i nated in a quartz-rich ma trix. The first spe cies (phase A) is rich in Al and may be recasted to K0.97(Mg1.52Cu1.05Fe0.21Ca0.20Ti0.01)S2.99(Si9.05Al5.88)S14.93(O,OH)
60.81-
n · mH2O (n = 7, 18 cat ions ba sis, nor mal ized by mul ti pli - ca tion per 1.05). A sin gle more silicic com po si tion (phase B, Ap pen dix 3, anal y sis 8) may be cal cu lated to K1.02(Mg1.42Cu1.20Ca0.22Ti0.18)S3.02(Al9.78Fe0.30)S1.08Si22.04(O,OH)125.33-n
× mH2O (36 cat ions ba sis). Yet an other spe cies (phase C, Ap - pen dix 3, anal y ses 9 and 10) may be ex pressed as (Cu1.70Ca0.12Mg0.03K0.04Fe0.01)S1.90(Si4.42Al0.11)S3.09(O,OH)21.77-n· mH2O (16 cat ions ba sis).
Sam ple BK2. Ex am ples of chrysocolla anal y ses are re - ported in Ap pen dix 2 (anal y ses 6–11). The wt.% ranges are 40.47–48.20 for SiO2, b.d.l. to 0.64 for Al2O3, 46.28–53.65 for CuO, and 0.22–0.46 for CaO. A sin gle anal y sis shows 0.30 wt.%
SO3 and 0.22 wt.% P2O5 – pos si bly an in ter fer ence. Recasted based on (Cu, Ca, Al) = 2 they give the empirical for mula (n = 25) of (Cu1.97Ca0.02Al0.01)S2.00(H0.01Si2.41O5)(OH)3.66 · 0.74H2O.
Just a sin gle anal y sis re casts to
(Cu1.99Ca0.02)S2.01(Si1.99S0.01O5)(OH)1.98 · nH2O which cor re - sponds to an “ideal” com pound of the for mula Cu2(Si2O5)(OH)2· nH2O (2 fewer hydroxyl groups be ing no ta ble).
Brochantite com po si tion (ex am ple anal y ses 1–10, Ap pen dix 4), is Cu4.00[(SO4)1.08(SiO4)0.05(PO4)0.01]S1.14(OH)5.61 (n = 17). Its com po nents vary in the fol low ing ranges (in wt.%): 0.19–0.79 SiO2, 59.82–70.94 CuO, 15.92–17.71 SO3, b.d.l. to 0.14 P2O5, and b.d.l. to 0.13 CaO This rel a tively large vari a tion is due both to dif fer ent lev els of sam ple de struc tion un der the elec tron beam and the min eral habit (i.e., lo cal po ros ity or thin ning).
Also, the sam ple seems to bear yet an other Cu sil i cate or a va - ri ety of chrysocolla. Ini tial an a lyt i cal re sults (Ap pen dix 3, anal y ses 11 and 12) sug gest the first spe cies, slightly de pleted in both Si and Cu (phase D), may have its pro posal for mula of (Cu0.79K0.14Fe2+0.08Ca0.02Ti0.01)S1.04(Al0.87Fe3+0.09P0.03)S0.99Si1.92[O5.67
(OH)1.33]S7.00 · nH2O (18 cat ions ba sis). The sec ond one (phase E, Ap pen dix 3, anal y ses 13–16) is pos si bly cal cu la ble to (K0.65Ca0.09)S0.74(Cu3.90Mg0.34Ti0.04)S5.09(Fe0.81Al0.19)S1.00(Si8.37Al3.51P0.09
S0.04)S12.01O28.04[(OH)0.96Cl0.05]S1.01 · nH2O (n = 5, same ba sis). As com pared to other min er als stud ied, both the phases D and E are Fe- and Ti-en riched, with max i mum con tents of up to 4.22 wt.%
FeO and 0.28 wt.% TiO2. They are also char ac ter ized by slight P (up to 0.49 wt.% P2O5) and Cl (up to 0.15 wt.%) en rich ment. Be - sides, phase E is en riched in S (up to 0.10 wt.% SO3). Of all the phases A–E, the high est amounts of K and Mg are found in phase A (up to 4.43 wt.% K2O and 7.37 wt.% MgO). The rather sta ble level of Cl en rich ment ex cludes ep oxy resin in ter fer ence.
Sam ple BK3-1. Con trol sam ples of a chrysocolla-like ma te - rial (Ap pen dix 2, anal y ses 12–14) show, on av er age, 47.81 wt.% SiO2, 3.69 wt.%, Al2O3, 39.12 wt.% CuO, 1.43 wt.% CaO, 0.16 wt.% MgO, 0.12 wt.% K2O, and 0.06 wt.% Cl. This chrysocolla is thus dif fer ent from the above ex am ples due to
slight en rich ment in K, Mg, and Cl. The anal y ses re cast to (Cu1.65Al0.24Ca0.09Mg0.01K0.01)S2.00(H0.24Si2.67O5)(OH) · nH2O (Cu + Al + Ca + Mg + K = 2 ba sis).
The brochantite com po si tion (n = 17, with ex am ple anal y ses 10–16 in Ap pen dix 4) is Cu3.97[(SO4)0.98(SiO4)0.03]S1.02(OH)5.86. This brochantite is slightly more pure than the above-de scribed one. Vari a tions of its com po nents, in wt.%, are: b.d.l. to 1.17 SiO2, 70.47–74.90 wt.% CuO, 16.98–18.20 SO3, and b.d.l. to 0.19 CaO.
The brochantite is as so ci ated with a slightly P-en riched phase that also bears trace Si and S. It is most likely mal a chite (Ap pen dix 5), es pe cially that CO3-PO4-SO4-SiO4 sub sti tu tion is known in min er als (e.g., in the ap a tite supergroup; e.g., Kruszewski, 2008). Its com po si tion is (n = 10) Cu2.00[(CO3)0.92(SO4)0.05(PO4)0.01(SiO4)0.01]S0.99(OH)2.00. Vari a - tion of its com po nents is as fol lows (in wt.%): b.d.l to 0.52 SiO2, 67.28–68.26 CuO, b.d.l to 3.81 SO3, and 0.17–0.53 P2O5.
Sam ple BK3-2. Two va ri et ies of a Cu-Si-O(H) phase were de tected, with rep re sen ta tive anal y ses in Ap pen dix 2 num - bered 15–17 (type 1) and 18–20 (type 2). The ob served vari a - tion of their con stit u ents, in wt.%, is 41.47–48.37 SiO2, 1.56–3.41 Al 2O3, 35.85–47.08 CuO, and 1.02–1.43 CaO. A sin gle anal y sis shows 0.02 wt.% ZnO and 0.50 wt.% K2O. As much as 2 in 13 anal y ses show a small P ad mix ture. Re cast - ing (n = 12 and n = 3, re spec tively) gives the fol low ing re sults:
–based on 4 to tal cat ions (in clud ing Si), to give the em pir i cal for mu lae:
(Cu1.55Al0.14Ca0.07)S1.76 (H0.14Si2.21O5)(OH)2.64 · 0.45H2O and (Cu1.40Al0.17Ca0.07)S1.64(H0.17Si2.34O5)(OH)2.98 · 0.09H2O –based on (Cu + Al + Ca) = 2, with the fol low ing em pir i cal for -
mu lae:
(Cu1.76Al0.16Ca0.09)S 2.01(H0.16Si2.48O5)(OH)4.26 and (Cu1.69Al0.21Ca0.09)S1.99(H0.21Si2.83O5)(OH)5.71Cl0.01; –based 2 Si at oms, to give the em pir i cal for mu lae:
(Cu1.39Al0.12Ca0.06)S1.57 (H0.12Si2O5)(OH)1.38 · 0.88H2O and (Cu1.20Al0.15Ca0.06)S1.41(H0.15Si2O5)(OH)1.12 · 0.65H2O;
–based on (Si + Al) = 2, with the fol low ing re lated for mu lae:
(Cu1.31Ca0.05)S1.36(H0.12Si1.89Al0.12O5)(OH)0.76 · 1.11H2O and (Cu1.11Ca0.06)S1.17(H0.14Si1.86Al0.14O5)(OH)0.34 · 0.95H2O Nei ther of these for mu lae fit the sup posed ideal chrysocolla con sti tu tion. Nor mal iz ing the wt.% re sults with the use of (Cu,Al,Ca) ox ides/SiO2 ra tios does not pose a large dif fer ence to the above for mu lae thus pro vid ing a likely con fir ma tion that at least the chrysocolla stud ied is not a sin gle com pound with pre - cisely at trib ut able ideal com po si tion.
Two sup posed chrysocolla anal y ses re cast to gilalite, (Cu4.81Ca0.14)S4.95(Si5.76Al0.27P0.02)S5.90[O16.92Cl0.02]S16.94 × 4.83H2O (ide ally Cu5Si6O17 × 7H2O; lower wa ter con tent pos - si bly due to de hy dra tion), but this spe cies was not con firmed via PXRD. An other mi nor phase ob served in the sam ple is a sup posed Fe-dom i nant Cu-bear ing alu mi no sili cate (Fig. 5F) with the fol low ing wt.% ranges: SiO2 8.14–8.75, TiO2
0.48–0.49, Fe2O3 76.73–77.77, Al2O3 1.12–1.26, CuO 5.04–6.02, CaO 0.31–0.39, MgO up to 0.17, Cl up to 0.06, and K, Mn, Zn, S, P, As, and V be low their de tec tion lim its.
With to tals >92% the phase can be recasted, e.g., to (Fe3+6.35Cu0.46Ti0.04Ca0.04Mg0.02)S6.91(Si0.94Al0.05)S0.99O12.06 · 2.45H2O (n = 3). How ever, tiny he ma tite crys tals are also found within voids in chrysocolla and the above anal y ses may sim ply be er ro ne ous due to pos si ble mixed-in for ma tion char ac ter.
S³awomir Mederski et al. / Geological Quarterly, 2021, 65: 43 7
DISCUSSION
PARAGENETIC SEQUENCE OF THE EPITHERMAL MINERALIZATION AT STARY LESIENIEC
At most lo ca tions known from the lit er a ture cop per sul phide paragenesis co ex ists with chal co py rite and bornite, which crys - tal lize at the first stages and then – with de creas ing tem per a ture – trans form into sim ple sulphides of the Cu-S sys tem (e.g., Hatert, 2005). In the hy dro ther mal sys tem at Stary Lesieniec undersaturated in iron, chal co py rite and bornite are ab sent.
The same is true for py rite which is oth er wise com mon in hy dro - ther mal sys tems. Most sim ple cop per sulphides, such as chalcocite, oc cur in ce men ta tion zones within supergene en - rich ment parts of var i ous cop per de pos its (e.g., Belogub et al., 2008; Vlasáè et al., 2018). At Stary Lesieniec, cop per sulphides are re lated to pri mary, epi ther mal min er al iza tion.
For ma tion stages and the paragenetic se quence of Cu min - er al iza tion at Stary Lesieniec are shown in Fig ure 6. At the hy - dro ther mal stage at the site stud ied crys tal li za tion be gan with idiomorphic quartz. Then, the main chalcocite masses were formed. Within the ag gre gates of chalcocite, uraninite also ap - peared. Uraninite in clu sions have also been found in the chrysocolla, which may in di cate that it crys tal lized within the lim - its of the epi ther mal stage. Ac cord ing to Pohjolainen (2015), the UO2
2 +(ura nyl) ions dis solved in hy dro ther mal flu ids run ning along faults may be de pos ited as uraninite in con tact with coun - try rocks. Youn ger than the chalcocite is djurleite, which formed ir reg u lar zones and inter growths with chalcocite.
The next stage is anilite/digenite for ma tion with the min er als de pos ited as elon gated lamellae along the cleav age planes of chalcocite and djurleite. The cop per-min er al ized zones were then filled with idiomorphic baryte crys tals, which are known
from many lo ca tions within the Intra-Sudetic Ba sin and Sowie Mts. (e.g., Kruszewski et al., 2019; Pršek et al., 2019; Mederski et al., 2020). Baryte crys tals are char ac ter ized by the pres ence of nu mer ous he ma tite in clu sions. Hy dro ther mal he ma tite is known (e.g., Dalstra and Guedes, 2004) and many pa pers de - scribe the hy dro ther mal syn the sis of this spe cies (e.g., Tadic et al., 2019). Sun et al. (2015), who char ac ter ized some BIF-type iron de pos its, men tioned a few habit va ri et ies of he ma tite, with a nee dle-like to fi brous one be ing a late-stage re place ment re - lated to fluid ac tiv ity. We thus sug gest the Stary Lesieniec he - ma tite is re lated to the hy dro ther mal ac tiv ity. Chrysocolla in the stud ied cop per-baryte min er al iza tion crys tal lized both at the epi ther mal and supergene stages; the in ter pre ta tion of the con - di tions of its for ma tion is de scribed be low.
Ura nium hy dro ther mal oc cur rences within the Intra-Sudetic Ba sin are known from the sec ond ary hematitization zones of rhyolites (e.g., Plewa, 1965; Migaszewski, 1972). Migaszewski (1972) de scribed pitch blende grow ing around py rite crys tals in por phyry from the Boguszów baryte de posit. More over, sim i lar min er al iza tion was de scribed from a bore hole within the sec - ond ary hematitization zone of the Up per Car bon if er ous Che³ miec rhyodacite laccolith. There, uraninite is in para ge - nesis with he ma tite, ga lena, and py rite (Migaszewski, 1972). In ad di tion, ura nium min er al iza tion is known from the Mieszko Coal Mine in Wa³brzych, where pitch blende oc curs in the con - tact zones of coal seams with the por phyry body, or in veins of dark grey and cherry-red do lo mite (Plewa, 1965). Pitch blende is there as so ci ated with do lo mite, sid er ite, marcasite, py rite, and sec ond ary ura nium and cop per min er als. Sylwestrzak (1972) pointed out that the av er age ura nium con tent of the Car bon if er - ous por phy ries (5.49 ppm) is sig nif i cantly higher than that in the Perm ian vol ca nic rocks (3.18 ppm) and is not re lated to the min - er al og i cal com po si tion of the rock. This in di cates sec ond ary hy - dro ther mal en rich ment in ura nium of these vol ca nic rocks.
More over, U en rich ment in the Žácleø and Glinik for ma tions within the Intra-Sudetic Ba sin is re lated to epigenetic ac tiv ity (Miecznik, 1989).
CRYSTALLIZATION TEMPERATURES OF THE EPITHERMAL PARAGENESIS AT STARY LESIENIEC
PXRD stud ies con firmed the pres ence of monoclinic low- chalcocite and the ab sence of hex ag o nal high-chalcocite in the sys tem stud ied. Ac cord ing to Ev ans (1981), the tran si tion tem - per a ture for these two poly morphs of chalcocite is 103.5°C (Fig.
7). There fore, the ini tial tem per a ture of the crys tal li za tion of cop per sulphides did not ex ceed 103.5°C. The pres ence of youn ger djurleite form ing ir reg u lar zones and re plac ing chalcocite in di cates a de crease in the crys tal li za tion tem per a - ture, the up per limit of sta bil ity of djurleite be ing 93°C (Fig. 7) (Ev ans, 1981). The youn gest Cu sul phide in the epi ther mal stage of the paragenetic se quence at Stary Lesieniec was anilite/digenite. The in ter pre ta tion of PXRD anal y ses tends to lead to anilite over digenite, even though the chem is try tends to be digenite. A mis match of the ob tained chem i cal for mula of anilite/digenite and the PXRD re sults is prob a bly due to the trans for ma tion of anilite into a phase sim i lar to digenite, as a re - sult of sam ple pol ish ing and dry ing (Morimoto et al., 1969;
Morimoto and Koto, 1970). Anilite is sta ble <70 ±3°C (Fig. 7) and, as a re sult of heat ing, it is de com posed and trans formed to high digenite and covel lite (Morimoto et al., 1969; Morimoto and Koto, 1970). The anilite de scribed by us crys tal lized in the con - di tions of the sta bil ity field for anilite and djurleite (Fig. 7). On the other hand, covel lite crys tal lized at the fol low ing, supergene stage (Fig. 7). In con clu sion, the cop per sul phide stud ied from
8 S³awomir Mederski et al. / Geological Quarterly, 2021, 65: 43
Fig. 6. For ma tion stages and the paragenetic se quence of Cu min er al iza tion in the Stary Lesieniec rhyodacite quarry
Stary Lesieniec be gan crys tal li za tion at tem per a tures of
~100°C, and then dur ing the epi ther mal stage of pre cip i ta tion, the tem per a ture of the so lu tions cooled to <72°C (Fig. 7).
The pres ence of uraninite is in ter preted as to its be long ing to the epi ther mal stage. Uraninite crys tal li za tion is usu ally re ported to take place at >200°C (e.g., Eriksson et al., 2004). Ac cord ing to Yuan et al. (2019), at 100–400°C, uraninite (hy dro ther mally de - pos ited at 250–450°C) dis solves and be comes a pre cur sor for the U4+ sil i cate min eral coffinite. The for ma tion of uraninite at low tem per a tures is fa voured by acidic con di tions (Cui et al., 2015).
Ad di tion ally, Rojkoviè et al. (1993) de scribed for ma tion tem per a - tures of Cu-U min er al iza tion from Novoveská Huta in Slovakia rang ing from 95 to 190°C. These tem per a tures were de ter mined for the youn ger Cu-U min er al ized veins that in ter sect older stratiform de pos its and host cop per min er al iza tion with uraninite and coffinite. The lower tem per a ture range for the Novoveská Huta min er al iza tion may cor re spond to the tem per a ture ranges of chalcocite for ma tion at Stary Lesieniec. The lo cal uraninite crys tal li za tion ei ther (1) pre ceded that of chalcocite, with pos si ble co-de po si tion, or (2) took place af ter the dis so lu tion of some ear - lier in clu sions. In deed, some marks of pos si ble in clu sion dis so lu - tion were ob served in the ma te rial stud ied. If the lat ter is true, then the Ca,Mn-dom i nant diadochy in the uraninite sug gests such pri mary in clu sions to be some car bon ate min er als which are well known for be ing a Ca, Mn-sink.
SECONDARY Cu MINERAL PARAGENESIS AND ITS FORMATION CONDITIONS
Chrysocolla is the most com mon sec ond ary min eral in the cop per-baryte min er al iza tion stud ied from Stary Lesieniec.
Farges et al. (2007) re de fined chrysocolla as a “mesoscopic as - sem blage com posed dom i nantly as spertiniite [Cu(OH)2], wa ter and amor phous sil ica (SiO2)”. How ever, other au thors do not sup port such find ings. They, e.g., state that chrysocolla is rather a cop per sil i cate col loi dal gel (Frost and Xi, 2013), or an
amor phous Cu sil i cate with some struc tural as pects re lated to those of tenorite and di op tase, but not Cu0 or cu prite (McKeown, 1994). The ex per i men tal stud ies of Hariu et al.
(2013) also sug gest the com pound to be a Cu sil i cate gel, with vari able Cu/Si mole ra tios, with PXRD im age pre clud ing sin - gle-crys tal study for de ter mi na tion of the struc tural model. Al - though Frost et al. (2012) seemed to con firm chrysocolla as a sep a rate min eral spe cies, they re ported false-cor rect (i.e., close to the “ideal” com po si tion) em pir i cal for mu lae as these are based on standardless EDX anal y ses with 100% to tal nor mal - iza tion. As such, the first au thor’s the ory is not nec es sar ily com - pletely wrong: var i ous chrysocollas may ex ist. This would ex - plain the large dis crep an cies be tween the pro posed em pir i cal for mu lae and the sup posed ideal for mula of chrysocolla. Nev er - the less, study ing its com po si tion (in par tic u lar, the Cu con tent) is rea son able due to the pro posed us age of this com pound as a Cu ore (e.g., Gijsemans et al., 2020). The Cu (alumino)sil i cate spe cies with rep re sen ta tive anal y ses listed in Ap pen dix 2 may be some new spe cies, or va ri et ies, of chrysocolla. We are aware of the fur ther anal y ses needed to be per formed for ei ther ap proval or disproval of such pro posal stoichiometry and site rep re sen ta tions.
The chrysocolla-bear ing paragenesis at Radzimowice, Lower Silesia, oc curs as thin encrustations in rhy o lite’s cracks (Siuda and Kruszewski, 2013). The au thors sug gested the rhy - o lite, and sur round ing rocks, as a source of sil ica. At Stary Lesieniec sil ica must have been de rived from the rock-ma trix aluminosilicates con tact ing with acidic so lu tions formed due to ox i da tion of the ore. Chrysocolla could have been formed via in - ter ac tion of such post-ox i da tion so lu tions, re leased sil ica, and me te oric wa ters al low ing for pH in crease (e.g., Schlomovitch et al., 1999). As the first sec ond ary weath er ing cop per min eral, chrysocolla re corded pH val ues most likely close to neu tral ones (e.g., Crane et al., 2001).
Ac cord ing to Frost et al. (2012), chrysocolla be gins to ther - mally de com pose at ~125°C. Thus, it should still be sta ble at the mod er ate/low-tem per a ture hy dro ther mal stage of min er al iza - tion. The up per-tem per a ture limit given for the Cu sulphides (103.5°C) is close to the one mark ing the ther mal sta bil ity of chrysocolla. The up per pH limit of the whole sec ond ary as sem - blage is sup ported by the com plete in ert ness of chrysocolla to leach ing at the pH of 6. Also, the min eral is eas ily leached at pH
<3 (Nikol and Akilan, 2018). On the other hand, Herrera-Urbina et al. (2010), who ad dressed the known pub lished is sue of chrysocolla flo ta tion, sug gested the re moval of sig nif i cant amounts of Cu from the min eral al ready at pH <6. Thus, the lo - cal chrysocolla sta bil ity may have been in the nar row 6–7 pH range. A fol low ing drop in pH al lowed for the re lease of Cu, most likely from both chrysocolla and some sulphides, and led to pre cip i ta tion of brochantite. Brochantite is the most sta ble hy - drous cop per sul phate min eral (e.g., Marani et al., 1995), with a rel a tively wide sta bil ity range of pH = 4–7.5 (Bridges and Green, 2007). How ever, the ab sence of langite and posnjakite sug - gests an up per pH limit of ~6 (Alwan and Wil liams, 1979). The min er al iz ing so lu tions of the supergene weath er ing stage must have been oc ca sion ally en riched in CO32 - ions, as re flected by the rare oc cur rence of mal a chite.
CONCLUSIONS
1. Ex am ples of cop per-baryte min er al ized veinlets were found cov er ing the west ern walls of the Stary Lesieniec rhyo - dacite quarry.
S³awomir Mederski et al. / Geological Quarterly, 2021, 65: 43 9
Fig. 7. Phase di a gram for the Cu-S sys tem in the low-tem per a ture re gion near Cu2S com po si tion;
adapted from Pot ter (1977) and Ev ans (1981)
2. A gen eral suc ces sion of crys tal li za tion for the epi ther mal stage is as fol lows: quartz–chalcocite–djurleite–anilite/dige - nite–ba ryte–he ma tite–chrysocolla; the supergene stage is rep - re sented by: chrysocolla + covel lite, fol lowed by brochantite + mal a chite.
3. The cop per sulphides stud ied be gan to crys tal lize at tem - per a tures of ~100°C; then, dur ing the epi ther mal stage of pre - cip i ta tion, the tem per a ture of the so lu tions dropped to <72°C.
4. The supergene ox i da tion pro cesses be gan with the for - ma tion of abun dant chrysocolla, at a rel a tively neu tral pH. Fol - low ing a pH drop, to ~4–6, brochantite was de pos ited. The min - er al iz ing so lu tions were only rarely en riched in car bon ate an - ions, as re flected by the rare oc cur rence of mal a chite.
Ac knowl edge ments. We are grate ful to A. W³odek from the Lab o ra tory of Crit i cal El e ments at AGH-UST and B. Marci - niak -Maliszewska from the Inter-In sti tu tion Lab o ra tory of Micro - analysis of Min er als and Syn thetic Sub stances UW for help dur - ing EPMA data col lec tion. We are also grate ful to the anon y - mous re view ers, whose com ments helped us to im prove the manu script. Also, the au thors would like to thank K. Pytel - who dis cov ered the Cu min er al iza tion stud ied – for shar ing this find with us. This work is part of the re search pro gram fi nanced by the AGH Uni ver sity of Sci ence and Tech nol ogy stat u tory grant No. 11.11.140.320 and 2020 stat u tory fund ing of the Min is try of Higher Ed u ca tion and Sci ence for the IGS PAS.
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