Geo log i cal Quar terly, 2018, 62 (2): 385–399 DOI: http://dx.doi.org/10.7306/gq.1414
Min er al og i cal, geo chem i cal and sta ble iso tope stud ies of ka olin de pos its in north-west Gonabad dis trict (east ern Iran)
Sedigheh ZIRJANIZADEH1, *, Fernando ROCHA2 and Somayeh SAMIEE1
1 Uni ver sity of Gonabad, Fac ulty of Sci ence, Ge ol ogy De part ment, Iran
2 Uni ver sity of Aveiro, Geobiotec Re search Unit, De part ment of Geosciences, 3810-193 Aveiro, Por tu gal
Zirjanizadeh, S., Rocha, F., Samiee, S., 2018. Min er al og i cal, geo chem i cal and sta ble iso tope stud ies of ka olin de posit in north-west Gonabad dis trict (east ern Iran). Geo log i cal Quar terly, 62 (2): 385–399, doi: 10.7306/gq.1414
Ka olin de pos its, sit u ated ~10 km north-west of Gonabad (east ern Iran), formed by the in tru sion of hy dro ther mal flu ids from a gran ite dyke in the west ern part of the study area, and the al ter ation of rhy o lite, dacite and rhyodacite re lated to Eocene vol - ca nism. There are four ma jor ka olin quar ries. The rocks in the in ves ti gated area are mainly slate, dacite, rhy o lite, an de - site-trachyandesite, and lithic and fel sic tuffs. The min er al og i cal com po si tions of the ka olin de pos its are dom i nated by quartz, kaolinite, dickite and illite with mi nor chlorite, mont mo ril lo nite, al bite, he ma tite, py rite and gyp sum. Sanidine and plagioclase crys tals in rhy o lite-rhyodacite are sericitized and kaolinized. Whole rock chem is try of the ka olin de pos its shows high con tents of SiO2 and Al2O3. En rich ments of Sr in some sam ples dem on strate re ten tion of Sr and de ple tion of Rb, Ba, Ca and K dur ing hy dro ther mal al ter ation of sanidine and plagioclase within the vol ca nic units. The chondrite-nor mal ized rare earth el e ment pat terns of the clay de pos its show LREE en rich ments (La/Lu)cn = 6.75 to 57.74, point ing to kaolinization in low-pH wa ters. The iso tope com po si tion of the ka olin (d18O ~+5‰) is con sis tent with for ma tion at iso to pic equi lib rium with wa ter of hy dro ther mal/mag matic or i gin. The min er al og i cal com po si tion, REE con tents and el e men tal ra tios in these de pos its sug gest prov e nance of the ka olin de pos its mainly from fel sic rocks and hy dro ther mal flu ids. The O iso to pic char ac ter also sup ports these re sults.
Key words: kaolinite, Iran, REE, O iso tope com po si tion.
INTRODUCTION
Hy dro ther mal kaolinite de pos its gen er ally de velop un der the con trol of an ac tive tec tonic en vi ron ment and with the pres - ence of per me able units, so that hy dro ther mal flu ids can cir cu - late through the rocks (Murray and Keller, 1993). In the study area, hy dro ther mal kaolinite de pos its typ i cally oc cur within vol - ca nic rocks. The area north-west of Gonabad is rich in clay min - er al iza tion (Miri Bidokhti, 2004; Gharibnavaz et al., 2007;
Miranvari et al., 2007). These de pos its are of eco nomic im por - tance. The re gion is lo cated in the north of the geotectonic Lut Block, be tween 58°33½–58°38½E and 25°34½–25°38½N (Figs.
1–4). Three large ka olin de pos its – Baghsiah, Rokhsefid (Fig.
5A), Yasmina, and a smaller one (Kalatehno) are lo cated within an area of ~7.5 km2. Baghsiah and Rokhsefid de pos its are the most im por tant sources of high-qual ity raw ma te rial (clay) for the ce ramic in dus tries in east ern Iran. These de pos its com prise a si lici fied zone (si lici fied cap) and a ka olin zone of other min er - als, be ing hosted by vol ca nic rocks such as rhy o lite and rhyodacite (Fig. 5B–F). Based on ASTER min eral map ping of this area it was pos si ble to iden tify min eral al ter ation zones.
Spec tral An gle Mappe (SAM) method (Kruse et al., 1993) is one of the best and eas i est tech niques for de lin eat ing the al ter ation zones. In other words, the most im por tant ca pa bil ity of sat el lites in min ing ex plo ra tion is to rec og nize al tered (es pe cially clay) min er als. Im age pro cess ing shows a wide range of clay min er - als (Fig. 2; Zirjanizadeh et al., 2011). To date, the geo log i cal, min er al og i cal and geo chem i cal fea tures (in the Baghsiah, Rokhsefid and Yasmina de pos its) have been stud ied with an em pha sis on tech no log i cal prop er ties (Miri Bidokhti, 2004;
Gharibnavaz et al., 2007; Miranvari, 2008). No de tailed min er al - og i cal and geo chem i cal stud ies have been done for the al ter - ation zones of ka olin de pos its, and the or i gin of geo ther mal so - lu tions re spon si ble for the hy dro ther mal al ter ations has not been in ves ti gated to date. The goal of the pres ent study was to im prove and in ves ti gate the geo log i cal, min er al og i cal and geo - chem i cal as pects as well as the gen e sis of hy dro ther mal kaolinite de pos its within Eocene vol ca nic rocks of Iran.
REGIONAL GEOLOGY
The study area is lo cated in the north ern Lut Block Zone (Fig. 1). Ac cord ing to Stocklin and Nabavi (1973), the Lut Block ex tends >900 km in a north-south di rec tion, from the Doruneh Fault in the north to the Jaz-Mourian Ba sin in the south, but it is only 200 km wide. The Lut Block is com posed of pre-Ju ras sic meta mor phic rocks and Ju ras sic sed i ments, in truded by dif fer -
* Corresponding author, e-mail: szirjanizadeh@yahoo.com Received: July 5, 2017; accepted: December 16, 2017; first published online: May 22, 2018
Fig. 1. Tec tonic sketch-map of Iran
The red rect an gle is the po si tion of the study area, and the larger box in di cates the lo ca tion of the Lut Block (com piled from: Berberian, 1981; Alavi, 1991)
Fig. 2. As ter min eral map ping shows a real dis tri bu tion of min er als in ter preted to be clay min er als in the area of in ves ti ga tions (Zirjanizadeh et al., 2013)
ent gen er a tions of Ju ras sic and Paleogene/Neo gene plutonic rocks, mainly granitoids, and cov ered by both ef fu sive and ex - plo sive Paleogene/Neo gene vol ca nic rocks rang ing from ba salt to rhy o lite in com po si tion. Vol ca nic and subvolcanic rocks of Paleogene/Neo gene age cover over half of the Lut Block. They are up to 2000 m thick and formed due to subduction prior to the col li sion of the Ara bian and Asian plates (Camp and Griffis, 1982; Tirrul et al., 1983; Berberian et al., 1999). In north-west Gonabad, epi ther mal sys tems are hosted in and formed con - tem po ra ne ously with Paleogene/Neo gene calc-al ka line vol ca - nic rocks that were erupted in a syncollisional set ting. The vol - ca nic prod ucts out crop along an 18 km long north- west–south - -east trending struc ture in north ern Gonabad.
LOCAL GEOLOGY AND ALTERATION IN CLAY DEPOSITS
Paleogene/Neo gene vol ca nic rocks host the ka olin de pos - its (Zirjani zadeh et al., 2013; Fig. 3). The rocks of this area com - prise slate, dacite, rhy o lite, trachyandesite, an de site, acidic tuff rocks and some subvolcanic in tru sions (por phy ritic monzonite and monzodiorite; Fig. 3; Zirjanizadeh et al., 2013). The old est unit (Shemshak For ma tion) is com posed of slate and quartz ite and is ex posed west of the area. Ju ras sic shale and sand stone have been al tered to slate and quartz ite by re gional meta mor - phism. Crys tal tuff out crops oc cur over most of the area (Fig.
6A). The vol ca nic units are grey ish-green, white and pink. Vol -
ca nic units of the Rokhsefid area con sist of dacite, rhyodacite, an de site and tuffs and have gradational con tacts with white to red dish white, mod er ately soft kaolinized and si lici fied zones.
The kaolinite de posit is cov ered by a hard sil ica cap zone (Fig.
5F and Ta ble 1). The sil ica cap is dark grey and has been brecciated. It shows sev eral stages of hy dro ther mal al ter ations with high sil ica con tent (Gharibnavaz et al., 2007). An de site - -rhy o lite tuffs are the main host rock of the Kalatehno de posit.
Ka olin min er als of this de posit are grey to yel low, mod er ately hard, and con tain py rite and Fe ox ides. XRD data con firms the pres ence and type of clay min er als in the de pos its (Fig. 7 and Ta ble 1). Vol ca nic rocks in the Baghsiah and Yasmina area con sist of trachyandesite, rhy o lite, dacite-rhyodacite, and green and pink ish tuffs. Rhyolitic, rhyodacitic and dacitic rocks are kaolinized. Petro graphi cally, the vol ca nic units have porphyric, trachytic and sieve tex tures. In an de site-trachyandesite, pheno - crysts in clude 25% plagioclase, 5% hornblende and 2% al kali feld spar al tered to seri cite (Fig. 6B). Groundmass com prises 30 to 35% plagioclase microlites and 10 to 15% opaque min er ali - sa tion. Car bon ates are rarely found within the plagioclase and in the ma trix – up to 10%. Chlorite (<3%) is scat tered. Trachyte is dis tin guished by trachytic tex ture. Sanidine forms 90% of this rock. Hornblende is filled by 3 to 5% of car bon ates; car bon ates can be also found as veinlets and in the groundmass – up to 2%. Other vol ca nic rocks in the area are dacite and rhyodacite.
Pheno crysts in clude 3 to 5% quartz, 7 to 10% plagioclase, 5%
hornblende and 1% bi o tite. The ma trix con tains 15% of sani - dine al tered to clay min er als (Figs. 4 and 6C). Monzonite por - phyry and quartz monzodiorite por phyry are ex posed at very Mineralogical, geochemical and stable isotope studies of kaolin deposit in north-west Gonabad district (eastern Iran) 387
Fig. 3. Geo log i cal map of clay de pos its area
few sites in the area. Po tas sium feld spar and plagioclase oc cur as pheno crysts. Al ter ations within these units are rep re sented by sili ci fi ca tion and sericitization (Fig. 6D, E). Ac ces sory min er - als are zir con and ap a tite. Fig ure 4 dis plays dif fer ent al ter ations in this area. The pri mary tex ture of the vol ca nic rocks ex posed in the quarry has not been ob served, but may be pre served in ar eas of less in tense al ter ation. An argillic al ter ation zone reaches 60 m in thick ness. The com mon min er als, as de ter - mined by X-ray dif frac tion stud ies (Miri Bidokhti, 2004;
Gharibnavaz et al., 2007; Miranvari et al., 2007), in clude kaolinite, quartz, K-feld spar, mont mo ril lo nite and illite. Main al - ter ation types are argillic, ad vanced argillic, propylitic and sili ci fi - ca tion with dif fer ent in ten si ties and form ing subzones. In di ca tor min er als of the ad vanced argillic zone in clude kaolinite, dickite, dia spore, seri cite, pyrophyllite and, in some places, quartz, alu - nite, py rite and tour ma line. For ma tion of min er als at this al ter - ation zone strongly de pends on hy dro ly sis, so lu tion tem per a - ture and min eral com po si tions of the host rocks. Hy dro ther mal fluid(s) flushed through fault and frac ture zones, and clay min - er als typ i cally were formed through the frac tures. The ka olin de - pos its are ori ented E–W. The main faults in this area are strike-slip faults, form ing spe cific types of the struc ture (Ghaemi, 2005).
MATERIALS AND METHODS
About forty thin-sec tions from the stud ied vol ca nic rocks were ex am ined un der the op ti cal mi cro scope. In or der to iden -
tify the dis tri bu tion of kaolinite and co ex ist ing clays in the vol ca - nic rocks, sam ples were col lected from four dif fer ent ka olin de - pos its. Clay min eral as so ci a tions have been stud ied us ing X-ray dif frac tion (XRD). X-ray di a grams were ob tained us ing a Philips An a lyt i cal X-Ray B.V. diffractometer. XRD anal y ses were per formed us ing CuKa ra di a tion and a scan ning speed of 1° 2q/min. The min eral com po si tion was de ter mined both on unoriented pow der mounts for bulk sam ple anal y ses and on ori - ented ag gre gates for the clay frac tion ones. The clay frac tions were sep a rated by sed i men ta tion ac cord ing to Stokes law, us - ing 1% so dium hexametaphosphate so lu tion to avoid floc cu la - tion. For the prep a ra tion of pref er en tially ori ented clay mounts, the sus pen sion was placed on a thin glass plate and air-dried.
Scans were run be tween 2° and 60° 2q (unoriented pow der mounts) or be tween 2° and 20° 2q (ori ented clay mounts) in the air-dry state af ter pre vi ous glyc erol sat u ra tion and heat treat - ment (300 and 500°C). Qual i ta tive and semi-quan ti ta tive min er - al og i cal anal y ses fol lowed the cri te ria rec om mended by Schultz (1964), Thorez (1976) and Mellinger (1979). For the semi-quan - ti fi ca tion of the iden ti fied prin ci pal min er als, peak ar eas of the spe cific re flec tions were cal cu lated and weighted by em pir i cally es ti mated fac tors, ac cord ing to Galhano et al. (1999), Oliveira et al. (2002) and Mar tins et al. (2007). SEM and EDX anal y ses were made us ing a Leo 1450VP scan ning elec tron mi cro scope at the cen tral lab o ra tory of Ferdowsi Uni ver sity of Mashhad.
Sam ples were pre pared by dis pers ing dry pow der on a dou - ble-sided con duc tive ad he sive tape. Then, the sam ples were coated with Au-Pd, 180 s, with a Sput ter coater SC7620 for SEM-EDX. Thirty-five bulk sam ples of fresh, mod er ately and highly al tered vol ca nic units (clay de pos its) were man u ally crushed and then ana lysed by wave length-dispersive X-ray Flu - o res cence (XRF) spec trom e try us ing fused discs and the Phillips PW 1480 XRF at the East Am e thyst Lab o ra tory in Mashhad, Iran, and for trace el e ments and rare-earth el e ments (REE) at ACME An a lyt i cal Lab o ra to ries Ltd., Van cou ver (Can - ada). Fluid-in clu sion stud ies were per formed on dou bly pol - ished sam ples taken from the si lici fied cap. Microthermometric de ter mi na tions were car ried out at the De part ment of Ge ol ogy, Ferdowsi Uni ver sity (Iran), us ing a Nikon Labophot-pol mi cro - scope mounted with a Linkam THMS-600 and TMS-92 freez - ing-heat ing stage. Four rep re sen ta tive kaolinite-bear ing sam - ples from highly al tered vol ca nic units (ka olin de pos its) were pu - ri fied and ana lysed for the ox y gen iso tope. Oxygene iso topes of kaolinite were mea sured in pu ri fied kaolinite. Kaolinite was pu ri - fied via sep a ra tion of the kaolinite (<2 µm) by sed i men ta tion, fol - lowed by centrifugation of the sus pen sion, and af ter the over - night dis per sion in dis tilled wa ter. The kaolinite par ti cles were dis persed by ul tra sonic vi bra tion for ~15 min utes. Ox y gen iso - tope com po si tion of pu ri fied sam ples was ana lysed in the Iso - tope Geo chem is try Lab o ra tory, Uni ver sity of Glas gow, Scot - land. All whole rock pow ders were ana lysed us ing a la ser flu o ri - na tion pro ce dure, in volv ing to tal sam ple re ac tion with ex cess ClF3 us ing a CO2 la ser as a heat source (in ex cess of 1500°C;
fol low ing Sharp, 1990). O2 re leased from the to tal flu o ri na tion of the sam ples was then con verted to CO2 by re ac tion with hot graph ite and then ana lysed on a VG Op tima mass spec trom e - ter. Ox y gen iso tope (d18O) val ues are re ported in the stan dard per mill (‰) no ta tion rel a tive to the Vi enna Stan dard Mean Ocean Wa ter (V-SMOW). Reproducibility is better than ±0.3‰
(1s) based on re peated anal y ses of in ter na tional and in-house stan dards run dur ing these anal y ses – UWG2, SES and GP147 – giv ing val ues of 5.9‰ (ver sus the ac cepted value of 5.8‰), 10.3‰ (ac cepted, 10.2‰) and 7.1‰ (ac cepted, 7.2‰) re spec tively, dur ing anal y ses of these sam ples. Con se quently, the ob tained val ues of anal y ses show that the nat u ral data are ac cu rate and pre cise.
Fig. 4. Al ter ation map of study area
RESULTS
MINERALOGICAL FEATURES (XRD, SEM/EDX ANALYSES)
The ka olin min er als oc cur as chalky-white, greasy and mas - sive bod ies, or as fine-grained frag ments or bod ies within highly al tered dacitic and rhyodacitic vol ca nic rocks and tuffs. The XRD pat terns of bulk sam ples in di cate that the ma jor min er als are quartz, kaolinite, dickite, illite, pyrophyllite, beidellite and nacrite.
Mi nor phases in clude alu nite, chlorite, mont mo ril lo nite, mus co - vite, al bite, he ma tite, py rite and gyp sum (Fig. 7 and Ta ble 1).
Ac cord ing to Fig ure 8, so lu tions form ing min er als in Kala - tehno have the pH rang ing be tween the sta bil ity of feld spars and kaolinite-pyrophyllite. How ever, the pH of so lu tions in Bagh siah, Rokhsefid and Yasmina are more acidic, and ka olin group min er - als formed. The SEM stud ies re vealed a range of clay min eral morphologies and fine-grained kaolinite crys tals (Fig. 9A). Some kaolinite par ti cles are <1 to 2 mm in size. The EDX spec trum shows the pres ence of Al, Si, and O along with mi nor con cen tra - tions of K and Fe (Fig. 9B). Some plate lets with hex ag o nal edges and book shapes were ob served as well, and the EDX spec trum shows that these small plate lets are com posed of Al, Si, and O (Fig. 9C). The par ent rocks are tuffs and rhy o lite-rhyodacite con - tain ing feld spar. Based on SEM/EDX stud ies, the al ter ation of Mineralogical, geochemical and stable isotope studies of kaolin deposit in north-west Gonabad district (eastern Iran) 389
Fig. 5. Field pho to graphs: A – a gen eral view of the Rokhsefid ka olin de posit; B – close-up view of supergene and hypogene clays from the Kalatehno de posit; the ef fect of me te oric wa ter on the top of hy - dro ther mal clays; C – close-up view of par tially al tered rhyodacite (coin size: 22 mm); D – sul phide min er - als (py rite) de vel oped within the kaolinized unit (coin size: 22 mm); E – gyp sum/anhydrite and iron-ox ide phases, along frac tures in su per fi cial parts of the Yasmina area; F – Rokhsefid kaolinite de posit and over - ly ing si lici fied rocks (rhy o lite and rhyodacite)
feld spar takes place in these epi ther mal en vi ron ments and kaolinite/dickite may have been formed from dis so lu tion of feld - spar.
Baghsiah and Rokhsefid ar eas. These ka olin min eral bod ies of var i ous thick nesses (rang ing from 50 m to >80 m) are lo cated next to each other. The sam pled hand spec i mens are mostly white, but they are seen also in yel low, or ange, brown and dark brown col our due to in crease of Fe and Ti ox ides (Ap - pen dix 1*). With the in creas ing amount of sil ica, the min eral sam ples are harder, rougher, and have sharp frac tured sur - faces, whereas the purer sam ples ap pear soapy to the touch and are soft and pow dery. He ma tite and py rite are ob served in the Baghsiah de posit. The min er al ogy of these de pos its is listed in Ta ble 1.
Yasmina area. Yasmina de posit com prises kaolinite, quartz, pyrophyllite and seri cite as main min er als, and chlorite, illite, mont mo ril lo nite, al bite and sanidine as ac ces sory min er als (Miranvari, 2008; Fig. 7 and Ta ble 1). Com par ing the min er al - og i cal com po si tion of Yasmina with Rokhsefid and Baghsiah, there are no he ma tite and py rite in Yasmina. There are large masses of gyp sum in some ar eas up to 20 cm or more, in the su per fi cial por tions.
Kalatehno area. The Kalatehno de pos its con tain quartz, illite, mus co vite, mont mo ril lo nite, al bite, orthoclase, gyp sum, py rite and he ma tite (Fig. 7 and Ta ble 1). The me te oric wa ter and hy dro ther mal flu ids re sulted in the for ma tion of two types of supergene and hy dro ther mal clays. The supergene clays
are de pos ited at the top of the hy dro ther mal clays; con se - quently, abun dances of these min er als de pend on sam ple lo - ca tion within the weath er ing pro file, and pre sum ably also on pri mary lithological vari a tions of the par ent rocks. For in - stance, feld spars de crease up wards and, by con trast, mus co - vite and/or illite in crease down wards in the ver ti cal pro file.
Coarse py rite is ob served in the Kalatehno area in vein and dis sem i nated forms, in com par i son with Yasmina, Rokhsefid and Baghsiah.
BULK-ROCK CHEMICAL FEATURES
Geochemically, the fresh vol ca nic rocks (par ent rock, Ap - pen dix 1) are rich in po tas sium, calc-al ka line in na ture, metalu - minous, en riched in LREE/HREE with LaN/YbN rang ing from 3.53 to 15.47, and show neg a tive Eu anom a lies (Ap pen dix 2).
Gen er ally, en rich ments in Al2O3 and SiO2 and de ple tions of K2O, TiO2 and CaO were dis cerned from fresh to mod er ately al - tered sam ples (Ap pen dix 1).
GEOCHEMISTRY OF MAJOR ELEMENTS IN CLAY DEPOSITS
Yasmina area. The SiO2 con cen tra tion in the Yasmina de - posit (Ap pen dix 1) is high (avg. 71.6%), but the amount of Al2O3
T a b l e 1 Min er al og i cal com po si tion of stud ied clay de pos its
(based on XRD anal y ses; Miri, 2004; Gharibnavaz et al., 2007; Miranvari et al., 2007, and this study)
Mine Sam ple X Y Ma jor phase Mi nor phase
Baghsiah BK51-2 649609 3810433 quartz kaolinite-mont mo ril lo nite
BK53-3 649693 3810331 quartz mont mo ril lo nite-kaolinite
Yasmina
Yass1 648925 3808237 quartz kaolinite-pyrophylite-mont mo ril lo nite
Kg47* 648700 3808237 quartz-kaolinite chlorite
Kg2* 647996 3808659 quartz-kaolinite mont mo ril lo nite-chlorite
Rokhsefid
A22 3810185 645193 quartz clinochlore, dickite
Ghar 645018 3810196 quartz clinochlore, dickite
EGA3* 645269 3810015 quartz mont mo ril lo nite
AW2* 645170 3810250 quartz kaolinite-mont mo ril lo nite
AL1* 645278 3810112 kaolinite-quartz mont mo ril lo nite-hydrohematite
AE5* 645224 3810173 kaolinite-quartz mont mo ril lo nite-he ma tite-cal cite
R22* 645118 3810366 quartz he ma tite
R33* 645130 3810324 quartz-alu nite kaolinite-he ma tite
Kalatehno
Geo1 643882 3813139 quartz-Illite-mus co vite
Geo2 643821 3813205 quartz-al bite-mont mo ril lo nite-palygorskite Geo3 643452 3813107 quartz-Illite-mus co vite
Geo4 643456 3813125 quartz-Illite-orthoclase-al bite Geo5 643456 3813125 quartz-mus co vite-orthoclase-
al bite-gyp sum
*Data for Rokhsefid mine from Gharibnavaz et al. (2007) and data for Yasmina mine from Miranvari (2008)
* Supplementary data associated with this article can be found, in the online version, at doi: 10.7306/gq.1414
is low (avg. 18.8%). The CaO value is low (0.7%) and the per - cent age of K2O is 2.2%. The to tal Fe (avg. 0.9%) and TiO2 con - tents (avg. 0.2%) are low.
Baghsiah and Rokhsefid de pos its. Clays from these de - pos its show av er age amounts of 20.5% Al2O3, 71.6% SiO2, 1.4%
Fe2O3 and 0.7% TiO2 (Ap pen dix 1). Be cause of high sil ica, the clays have high rough ness. TiO2 is as much as a max i mum of 1.5% in Rokhsefid, whereas it is be tween 0 to 1.5% in the other de pos its. K2O con tent is neg li gi ble. The pres ence of alu nite be - low wa ter ta ble shows that me te oric wa ters have leached K2O
and alu nite formed. Oc cur rence of alu nite in di cates an acid en vi - ron ment with a pH be tween 2 and 4 (Hemley et al., 1969;
Stoffregen, 1987; Fig. 7 and Ta ble 1; sam ple no: R33).
Kalatehno area. Chem i cal anal y ses of whole rocks re - vealed high per cent age of SiO2 (avg. 61.0%) and low amount of alu mina (avg. 17.7%); K2O (avg. 4.1%) re flects the pres ence of illite and K-feld spar (Ta ble 1; Ap pen dix 1). The av er age SiO2
con tent (61.0%) in Kalatehno is lower than that in Yasmina (71.6%) and Rokhsefid (64.5%) and higher than the av er age in Baghsiah (55.2%).
Mineralogical, geochemical and stable isotope studies of kaolin deposit in north-west Gonabad district (eastern Iran) 391
Fig. 6. Pho to mi cro graphs
A – tuff with groundmass al tered to argillic (PPL); B – al tered feld spar within an de site (XPL); C – plagioclase al tered to clay min er als in rhyodacite (XPL); D – sili ci fi ca tion, seri cite and opaque min er als in quartz monzonite por phyry (XPL);
E – plagioclase crys tals are bro ken and filled by cal cite; quartz has grown in the mar gins of plagioclase; PPL – plane-po lar ized light; XPL – cross-po lar ized light; Pl – plagioclase; Py – py rite; Qtz – quartz
Fig. 7. X-ray dif frac tion pat terns for sam ples from ka olin de pos its
Pyro – pyrophyllite, Kao – kaolinite, Mus – mus co - vite, Ill – illite, Clch – clinochlore, Qtz – quartz, Mont – mont mo ril lo nite, Plg – plagioclase, Ab – al bite, ab - bre vi a tion of min er als from Whit ney and Ev ans (2010)
GEOCHEMISTRY OF TRACE ELEMENTS IN DEPOSITS
In or der to in ves ti gate the geo chem i cal con di tions of the hy - dro ther mal so lu tion and its or i gin, the be hav iour of trace el e - ments was in ves ti gated dur ing the pro cess of kaolinization (Ap - pen dix 2).
REE pat terns (Fig. 10) show an en rich ment of LREEs in re - la tion to HREE. En rich ment of Sr (Ap pen dix 2) dem on strates re ten tion of Sr and de ple tion of Rb, Ba, Ca, and K dur ing al ter - ation of sanidine and plagioclase within the vol ca nic units. Sr con tent may be re lated to the for ma tion of mus co vite and partly to K-feld spar re place ment of pri mary plagioclase.
The neg a tive Eu anom aly (Fig. 10A) sug gests al ter ation of feld spar at high tem per a ture and re lease of Eu+2 dur ing di - min ish ing hy dro ther mal al ter ation (Lackschewitz et al., 2000). Chondrite-nor mal ized pat terns for the Rokh sefid mine (Fig. 10B) show a pos i tive Eu anom aly that is re lated to the pres ence of calcic plagioclase in the source.
Mineralogical, geochemical and stable isotope studies of kaolin deposit in north-west Gonabad district (eastern Iran) 393
Fig. 8. Sta bil ity di a gram of ka olin min er als, K-feld spar and an da lu site at dif fer ent tem per a tures and pH
(Montoya and Hemley, 1975)
1 – Kalatehno, 2 – Yasmina, 3 – Rokhsefid, 4 – Baghsiah
Fig. 9. SEM im age of min er als from ka olin de pos its A – feld spar crys tals with kaolinite oc cur - rences in Yasmina de posit (no. Yass1);
B – SEM im age of hex ag o nal (book - -shaped) kaolinite crys tals and EDX anal y sis of marked rect an gle (Yasmina de posit; no. Yass1); C – SEM/EDX of Rokhsefid (no. R33)
FLUID INCLUSION MICROTHERMOMETRY AND STABLE O ISOTOPE SIGNATURE
All of the in ves ti gated sam ples con tain pri mary fluid in clu - sions us ing the def i ni tion of Roedder (1984). Pri mary fluid in clu - sion pop u la tions are dom i nated by liq uid-vapour two-phase. In pri mary fluid in clu sions, the ho mog e ni za tion tem per a tures range from 186 to 326°C (Fig. 11). If fluid in clu sions were <5 µm in size, con se quently, the sa lin ity was not mea sured.
The d18O val ues of four nearly pure kaolinite sam ples are listed in Ta ble 2. The sta ble iso to pic com po si tion of min er als de - pends on the iso to pic value of the par ent flu ids from which they were formed (e.g., Savin and Ep stein, 1970; Murray and Janssen, 1984; Sheppard and Gilg, 1996). The iso to pic frac tion - ation fac tor (a) be tween kaolinite and wa ter is shown to be 1000 ln a kaol-wa ter = 2.76 ×106 T-2 – 6.75 (Sheppard and Gilg, 1996).
Based on a fluid in clu sion study of hy dro ther mal quartz, the hy dro ther mal min er als in this area formed at tem per a tures be - tween 250 and 350°C. The d18O val ues cal cu lated for the co ex - ist ing wa ter (2.9 and 7.6‰, Ta ble 2 and Fig. 12) are con sis tent
with kaolinite for ma tion at iso to pic equi lib rium with hy dro ther - mal/mag matic wa ter, yield ing tem per a tures up to 250°C.
DISCUSSION
Argillic al ter ation ex hib its lat eral and ver ti cal zonation that can be di vided into min eral as sem blages. These as sem blages were as fol lows: si lici fied zone (sil ica cap), quartz + ka olin min - er als + alu nite zone, and K-feld spar + illite + mont mo ril lo nite zone.
Si lici fied zone: in all quar ries, this zone of the de posit oc curs in three dis tinct si lici fied set tings: within fault zones, in sil ica cap rocks, and as si lici fied rocks. At fault zones and si lici fied rocks, quartz was ac com pa nied by kaolinite min er als. In the Yasmina de posit, sil ica-filled fault zones were 5 m in width, and ~1000 m in length. Mas sive dark sil ica caps oc curred at Baghsiah and Rokhsefid. Based on field ob ser va tions, si lici fied rhyolitic tuff and quartz monzonite por phyry rocks (si lici fied rocks) were ex - posed in the Kalatehno de posit.
Fig. 10. Chondrite-nor mal ized REE pat terns of bulk rock
A – chondrite REE con cen tra tions (from An ders and Grevesse, 1989), B – chondrite REE con cen tra tions (from Haskin et al., 1968) and Rokhsefid de posit data
from Gharibnavaz et al. (2007)
Quartz, ka olin min er als + alu nite zone: con tained quartz, kaolinite, dickite and alu nite. This min eral as sem blage oc curred out ward and down ward the fault zones. This al ter ation zone rep - re sented the eco nomic part of the de pos its. The mas sive and white, yel low and or ange kaolinite de posit ex tended ver ti cally and lat er ally lon ger than 50 × 3000 m, lon ger than 60 × 1800 m and lon ger than 30 × 1200 m at the Rokhsefid, Baghsiah and Yasmina mines, re spec tively. XRD anal y ses in di cated that quartz and kaolinite are the ma jor min er als in this zone.
K feld spar + illite + mont mo ril lo nite zone: con tained feld spar + illite + mont mo ril lo nite. In the Kalatehno de posit, monzonite por phyry and tuffs were de stroyed due to lower in ten sity of chem i cal re ac tions of acidic geo ther mal and me te oric wa ters.
Rel ict rock tex tures and K-feld spars were ob served in the thin- sec tions of monzonite por phyry (Fig. 6D). Model for the epi ther - mal sys tem re lated to the ka olin de pos its in study area shows the for ma tion and al ter ation zones of the de pos its (Fig. 13).
Clays from the stud ied de pos its typ i cally con tain 55.9–85.13% SiO2. A high SiO2 con tent is re lated to the pres - ence of opal and chal ce dony in the sil ica cap zone, which co ex - ist with ka olin, and is the re sult of wide spread sili ci fi ca tion within the de pos its.
Cor re spon dence be tween geo chem is try and min er al ogy data shows that the K2O (0–6.1%) and MgO (0.05–1.1%) con - tents (Ap pen dix 1) in di cate co ex is tence of illitization and kaoli - nization. The sig nif i cant value of K2O con tent in the Kalatehno de posit (6.1 wt.%) cor re lates with the en rich ment in mus co - vite/illite in the bed rock from which it is de rived.
Mineralogical, geochemical and stable isotope studies of kaolin deposit in north-west Gonabad district (eastern Iran) 395
T a b l e 2 O iso to pic com po si tion of kaolinites and cal cu lated O iso tope com po si tion of co ex ist ing aque ous spe cies
Sam ple
(lo cal ity) Min eral As so ci a tion Min eral Mea sured d18O(‰)
Cal cu lated tem per a ture [°C]
Cal cu lated com po si tion of wa ters [avg. ‰]
BK51-2
(Baghsiah) quartz-mont mo ril lo nite kaolinite 6.3 250–300 3.2
300–350 4.5
A22 (Rokhsfid) quartz-clinochlore-dickite kaolinite 6.8 250–300 2.9
300–350 4.26
Yass1 (Yasmina) quartz-pyrophyllite-
mont mo ril lo nite kaolinite as so ci ated
with dickite 6 250–300 2.9
300–350 5.06
Ghar (rokhsefid) quartz-clinochlore-dickite kaolinite as so ci ated
with dickite 9.3 250–300 6.2
300–350 7.56
Fig. 11. His to grams show ing the ho mog e ni za tion tem per a tures of pri mary in clu sions
Fig. 12. d18 com po si tions of cal cu lated equi - lib rium wa ter at 200–250°C and 300–350°C Range of mag matic wa ters from Sheppard and Gilg (1996), range of me te oric wa ter from Craig (1961), range of for ma tion wa ter from Hoefs (2004) and range of meta mor phic wa ter from Tay - lor (1979)
Higher amounts of Fe ox ides in the sur face, as com pared to deeper zones, in di cate that Fe ox ides were washed out of the rocks (tuffs and rhyolites con tain ing py rite and Fe ox ides) and in jected into joints and frac tures in sur face parts. The Fe2O3
value in some sam ples (e.g., Al1, Omid 1; Ap pen dix 1) is re - lated to iron-ox ide and iron-sul phide phases, such as he ma tite and py rite. These Fe ox ides stained ka olin min er als. The red - dish-brown colour ing in the sil ica cap is also due to the pres - ence of Fe ox ides.
The dis tri bu tion of ma jor el e ments points to rel e vant compo sitional changes. Such changes are char ac ter ized by loss of the al ka lis (CaO, MgO, Na2O and K2O; Figs. 14A, B and 15) and en rich ment of Al2O3 (Figs. 14C and 15) in ad di tion to in - creas ing wa ter, as refected by loss on ig ni tion (LOI), so pri mary Ca-, Na- and K-bear ing sil i cates were leached and re placed by newly -formed Al-rich clay min er als and sulphates (Kara kaya, 2009).
In crease in al ter ation in ten sity is cou pled with a grad ual de - crease in Fe2O3 + MgO and Na2O + K2O con -
tents (Fig. 14A, B). The Na2O + CaO con tents in par ent and mod er ately al tered rocks are 5.7–7.2% and 0–8.2%, re spec tively. Fe2O3 + MgO and Na2O + K2O con tents are dif fer ent in com pletely al tered sam ples, es pe cially in the Rok hsefid and Baghsiah rather than in the Yasmina and Kalatehno de pos its. They are be - tween 0 and 0.6%, show ing that more leach ing oc curred dur ing the hy dro ther mal pro cesses.
Fig ure 15 dis plays de struc tion of plagio - clase and K-Feld spar and de vel op ment of kaolini zation. Con se quently, the cir cu la tion of sil ica-rich geo ther mal flu ids along the flow path within the in ter me di ate and fel sic rocks leach the al ka line and al ka line earth el e ments of rock.
In ad di tion, due to de creas ing of pres sure and tem per a ture, which oc cur near the sur face, rapid pre cip i ta tion of sil ica is fa voured and si lici - fied rocks are the re sult of neu tral iza tion of pH (Karimpour and Saadat, 2005).
These geo ther mal flu ids orig i nated from a gran ite dyke that is ex posed out side the area.
They were trans ported through a fault sys tem (Fig. 13). The brec cia sil ica cap re veals that kaolinization oc curred in sev eral pe ri ods dur ing the hy dro ther mal al ter ation pro cess.
Hy dro ther mal flu ids trans ported through frac - ture zones re sulted in an in crease in Al2O3/SiO2
(Fig. 14C) ra tios, fa vour ing pre cip i ta tion of kaolinite un der acidic con di tions (Meunier, 1995; Kadir and Ka rakaº, 2002; Felhi et al., 2008). In con trast, the con cen tra tion of al ka line el e ments and Al2O3 + Fe2O3 + MgO re sulted in an al kali con di tion suit able for the pre cip i ta tion of smectite (Weaver, 1989; Chamley, 1989;
Christidis et al., 1995; Kadir et al., 2011). The as so ci a tion of kaolinization with sili ci fi ca tion, Fe-ox i da tion, and the pres ence of py rite and gyp sum, sug gest hy dro ther mal al ter ation pro cesses in the vol ca nic rocks.
Fol low ing the ef fects of hy dro ther mal flu ids in the area, sec - ond ary leach ing has been caused by me te oric wa ter, and re - sults in supergene min er als in the Kalatehno de posit (Fig. 5B).
Con se quently, the me te oric wa ter and hy dro ther mal flu ids caused two types of supergene and hypogene zones in which supergene clays are de pos ited on top of the hypogene clays.
The min er al ogy of supergene clays com prises quartz, illite, mus co vite and gyp sum (Ap pen dix 1; Fig. 16). Their rel a tive abun dance de pends on the sam ple lo ca tion within the weath er - ing pro file, and pre sum ably pri mary lithological vari a tions of the par ent rocks (quartz monzonite por phyry, Fig. 5D). Feld spars de crease up wards in the pro file and ap pear to be re placed by clays in the up per most weath ered sam ples (Fig. 16).
On an A-CN-K di a gram (Fig. 15; Nesbitt and Young, 1984), most of the sam ples plot at the Al2O3 –(CaO + Na2O) bound ary.
At this point, K has been leached from the rocks (i.e. K-feld spar de stroyed), re flect ing the lack of feld spars and abun dance of aluminous clay min er als (e.g., kaolinite, halloysite). Pri mary min er als have been de creased, es pe cially in Rokhsefid, Baghsiah and then Yasmina and Kalatehno.
LREE en rich ments [(La/Lu)cn = 6.75 to 57.74] im ply that kaolinization oc curred in low-pH wa ters (Bau, 1991; Nyakairu et al., 2001) and that weath er ing af fected these de pos its (Lackschewitz et al., 2000). The change of Eu anom aly from pos i tive to neg a tive and the ex tent of neg a tive Eu anom aly are cor re lated with the de gree of plagioclase de com po si tion. The neg a tive Eu anom aly in Baghsiah, Kalatehno and Yasmina Fig. 13. Mod els for the epi ther mal sys tems re lated to kaolinite
de pos its at north-west Gonabad
Fig. 14A – FeO + MgO vs. SiO2 di a gram; B – Na2O + K2O vs. SiO2 di a gram;
C – Al2O3 vs. SiO2 di a gram
sam ples is most prob a bly re lated to plagioclase weath er ing, where most Eu is hosted. The pos i tive Eu anom aly in Rokhsefid sam ples may be caused by Eu con cen tra tion in hy dro ther mal clay min er als, like illite and illite-smectite, af ter their re lease from plagioclase to the geo ther mal fluid. The weak neg a tive Ce anom a lies in sam ples may be re lated to the for ma tion of Ce4+
un der ox i diz ing con di tions of near-sur face en vi ron ments while other REE re main tri va lent (Braun et al., 1990; Class and la Roex, 2008). The sam ples show ing neg a tive Ce anom a lies prob a bly also re flect frac tion ation of Zr (Karakaya, 2009). Zr con tent in creases with in creas ing Ce con tent (e.g., sam ple no:
KN-Geo-1, Ap pen dix 2).
Clays are re sis tant to post-formational iso to pic ex change at near-sur face sys tems (Savin and Hsieh, 1998). There fore, it can be as sumed that the ka olin min er als may re tain their orig i nal iso tope sig na ture (Fig. 12). Based on iso to pic val ues, we can con sider that kaolinite was formed by hypogene mag - matic-hy dro ther mal ac tiv ity. An acid en vi ron ment with low pH caused the oc cur rence of kaolinite. Ob vi ously, at low pH, hy - dro gen ions in hibit the poly mer iza tion of dis solved sil ica (Fournier, 1985). There fore, neu tral iza tion of the flu ids was re - quired to cause sil ica pre cip i ta tion in the form of opal (Sillitoe, 1993).
The as so ci a tion of kaolinite with sil ica min er als and alu nite in these de pos its cor re sponds to a typ i cal min eral suite of ad - vanced argillitic al ter ation. Sim i lar al ter ation sys tems are as so - ci ated with the de po si tion of pre cious met als (Hayba et al., 1985; Stoffregen, 1987; Arribas et al., 1995). The hy dro ther mal ac tiv ity in these ar eas shows min er al og i cal and geo chem i cal fea tures (As, 10 ppm; Sb, 4–38 ppm; Ghaemi, 2005) typ i cal of an epi ther mal en vi ron ment.
CONCLUSIONS
The stud ied ka olin de pos its formed by hy dro ther mal al ter - ation of vol ca nic rocks re lated to the Eocene vol ca nism in the Lut Block. The vol ca nic units con sist of rhy o lite, rhyodacite, dacite, trachyandesite, an de site and tuff. The ka olin de pos its con tain quartz, kaolinite, dickite, illite, pyrophyllite, mont mo ril lo - nite, mus co vite, gyp sum and iron-ox ide and iron-sul phide phases (py rite, he ma tite). Our main con clu sions are:
(1) The area con tains meta mor phic rocks, rhy o lite, dacite - -rhyodacite, trachyte, an de site–trachyandesite, tuffs and some subvolcanic rocks. Vol ca nic rocks have been af fected by acidic hy dro ther mal flu ids. The source of these flu ids is a gra nitic dyke that was ex posed in the west ern part of the study area and in - truded into the Shemshak For ma tion. Based on the ori en ta tion of faults and kaolinization, these al ter ation pro cesses were con - trolled by tec tonic ac tiv ity.
(2) These de pos its com prise a si lici fied cap and an illite - -smectite, kaolinite and Fe ox ides zone that is hosted by vol ca nic rocks. De vel op ment of a sil ica cap on kaolinized zones sug gests hy dro ther mal ac tiv ity. Hy dro ther mal al ter ation is sup ported also by the oc cur rence of and iron-ox ide and iron-sul phide phases (such as he ma tite and py rite). Evaporitic min er als (mainly sulpha tes) are pres ent in the sur face parts of clay de pos its.
(3) Clay de pos its are char ac ter ized by 59-85.1% SiO2, 12.2–29.1% Al2O3, 0.5–2.0% Fe2O3, 0.01–6.1% K2O, and 0.05–1.1% MgO. Kaolinite is as so ci ated with quartz, pyro - phyllite, illite, he ma tite, mont mo ril lo nite, py rite, gyp sum and some mi nor phases. The al ter ation types are char ac ter ized by an in crease in Al2O3 and Sr, and de ple tion in Fe2O3, CaO, MgO and partly K2O. En rich ment in LREE and neg a tive Eu anom a - lies (in Kalateno, Baghsia and Yasmina de pos its) re veal that frac tion ation of feld spar oc curred dur ing al ter ation. How ever, a pos i tive Eu anom aly in some mod er ately al tered and Rokhsefid sam ples (com pletely al tered rocks; Ap pen dix 1, Fig. 10B) in di - cates that plagioclase was not al tered sub stan tially and the re - main ing was REE pres ent in the al tered min er als.
(4) Geo chem i cal and min er al og i cal char ac ter is tics in di cate that the hy dro ther mal flu ids that formed the ka olin de pos its were acidic, and ox i da tion.
(5) Al ter ation de vel oped in a high-tem per a ture hy dro ther - mal pro cess. The sta ble iso tope sig na ture of the kaolinite and dickite (an av er age value of 5‰) re flects for ma tion un der the in - flu ence of hy dro ther mal-mag matic wa ter ac tiv ity.
Ac knowl edge ments. The au thors wish to thank Mrs.
A. Quintela (Uni ver sity of Aveiro, Por tu gal) for the as sis tance dur ing sam ple prep a ra tion for XRD anal y sis and guid ance in in - ter pre ta tion. Thor ough and con struc tive re views by Prof. Ö.
Ece, Dr. P. Brañski, Anon y mous Re viewer and Chief Ed i tor Prof. T.M. Peryt are much ap pre ci ated.
Mineralogical, geochemical and stable isotope studies of kaolin deposit in north-west Gonabad district (eastern Iran) 397
Fig. 15. Tri an gu lar Al2O3-(CaO + Na2O)-K2O plot di a gram (Nesbitt and Young, 1982)
Ka – kaolinite, Gb – gibbsite, Chl – chlorite
Fig. 16. Ver ti cal dis tri bu tion of ma jor min er als in the Kalatehno de posit; depth of the sam pling point (in metres)
is in di cated by the dig its to the right of the sam ple name
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Mineralogical, geochemical and stable isotope studies of kaolin deposit in north-west Gonabad district (eastern Iran) 399
