Topuk-Göynükbelen (Orhaneli-Bursa) yöresi nikel oluşumlarının kökensel incelenmesi

Abstract

ÖZET Topuk-Göynükbelen(Orhaneli-Bursa) yöresi nikel oluşumları ve bu oluşumlardan sorumlu Göynükbelen granitoyid sokulumu ile ultramafik kayaçlar mineralojik ve jeokimyasal acıdan ele alınarak incelenmiştir. Sahadaki nikel oluşumları, Paleojen yaşlı sokulumdan kaynaklanan hid- rotermal çözeltilere bağlı olarak, Üst Kretase-Paleosen yaşlı ultra mafik kayaçlardaki kırık ve çatlakların kontrolünde meydana gelmiştir. Kalk-alkali granitik bir magmanın ürünü olan Göynükbelen grani toyid sokulumu, göreceli olarak sodik karakterlidir. QAP üçgen diyag ramında diyorit-gabrD, kuvars diyorit, kuvars monzodiyorit, tonalit ve granodiyorit alt birimlerini içeren sokulum, I- tipi granitoyidlerin mineralojik ve kimyasal özelliklerini sergilemektedir. Tektonik disk- riminasyon diyagramında volkanik yay granitoyidlerinin alanında yer alan sokulum, primitif ada yayları ve kıtasal yaylardan, normal kıta sal yaylara kadar geniş bir yay olgunluğu göstermektedir. Dunit, harzburjit, piroksenit damarları, piraksenli gabro, serpantinit ve listvenit oluşumlarını içeren ultramafik-mafik birimin, baskın kayaç tipleri, değişen oranlarda serpantinleşmiş dünit ve harzburjitlerdir. Mg0-A1_D3 ve MgO-CaO diyagramlarında az tüketilmiş pirolit alanında yer alan ultramafik-mafik kayaçlar, AFM üçgen diyagramında mafik-ult- ramafik kümülat ve ultramafik tektonik sınırları içinde yayılım gös termişlerdir. Çalışma alanında yukarıda tanımlanan koşullara bağlı olarak mey dana gelmiş üç farklı tip nikel oluşumu tespit edilmiştir. Bunlar: 1- Serpantinleşmiş ultramafik kayaçların yerli yerinde (in situ) ay- rışmasıyla meydana gelmiş, kırmızı toprak znnlardaki nikel zenginleş meleri. Arazide düzensiz bir dağılım gösteren ve ortalama 3m. düşey kalınlığa sahip olan bu zonlarda, en düşük 1DD ppm., en yüksek 9DD0ppm. Ni değerleri elde edilmiştir. 2- Göynükbelen granitoyid sokulurundan kaynaklanan hidrotermal çözel tilerin içlerinden geçtikleri ultramafik kayaçlardan remobilizasyonla kazandıkları nikel 'i yine ultramafik kayaçlardaki kırık ve çatlaklar içine pentlandit, hezlavudit, millerit, makinavit, avaruit ve viyola- rit şeklinde çökelmesiyle oluşan nikel sülfür oluşumları. Bu tür olu şumlar arazide beş zonda tanımlanmıştır. Yüksek nikel değerleri, saha nın güneyinde Meryemkaldırımı Sırtı ile YapkBy Dere 'den alman örnek lerde saptanmıştır. 3- Nikel sülfür oluşumlarından sorumlu hidrotermel çözeltilerin taşı dığı Nikel 'in (Ni ), ortaşda var olan talk ve klorijler'in kristal yapısındaki magnezyum (Mg ) ve kısmen demir' in (Fe ) yerini alma sıyla (substitution) oluşan nikelli talk, nikelli kloritleşimş talk ve nikelli kloritler. Arazinin güneyinde yaygın alarak bulunan ve yeşil renkli pulcuklar şeklinde izlenen bu tür oluşumlar genelde ni kel sülfür oluşumlarıyla birlikte bulunmaktadır. Laboratuvar araş tırmaları sonucu, bu tür nikel oluşumlarının, talk ve kloritlerin fi ziksel ve kimyasal özellikleri arasında özelliklere sahip bir ara ürün olduğu sonucuna varılmıştır. vı

GENETICAL INVESTIGATION OF NICKEL OCCURRENCES IN THE VICINITY OF TOPUK-GÖYNÜKBELEN, ORHANELİ-BURSA SUMMARY This study deals with the Topuk-Göynükbelen (Drhaneli-Bursa) nickel mineralizations of Nld-Anatolia. Together with this occurrences, mineralogical and geochemical investigations of the ultramafic rocks and Göynükbelen granitoid intrusion, responsible of nickel formations, were carried out. The research area is covered by different rock- units of various ages, Which are, beginning from the oldest rock-type. 1 - Metamorphic unit which is made of metamorphic rocks of the Paleozoic - Mesozoic age and the Paleozoic Çatalca Tepe marbles.. This unit was metamorphosed under High Pressure/Low Temperature (HP/LT) conditions. Metamorphic rocks of the Paleozoic-Mesozoic age consist of essentially, quartz-muscovite schist, chlorite- epidote-glaucophane schist, calc schist, graphite-mica schist and metabasite and in lesser amount limestone, and serpentinite blocks. 2- Maf ic-ultramaf ic unit of the Upper Cretaceous- Paleocene age. This unit embraces rocks like dunite, harzburgite, serpentinite, pyroxene-gabbro and listvaenites. Some granitoid dykes or anclaves have also been determined within this unit. 3- Göynükbelen granitoid intrusion of Paleogene aga. This intrusion seems to intrude through metamorphic basement rocks of The Paleozoic-Mesozoic and ultramafic and mafic rocks of The Upper Cretaceous- Paleocene age. Maf ic-Ultramaf ic blocks of diffrent Vlldimensions were observed in the intrusive unit which essentially comprises diorite- gabbro, quartz diorite, quartz monzodiorite, tonalite and granodiorite. k- The Neogene Sedimentary unit resting on ultramafic rocks. This unit is made of boolders of ultramafic and granitoid rock, basal conglomerate, coarse sand and marl. Within this unit thin coal seams and tuffeceous bed alternations have also been determined. Topuk-Göynükbelen nickel occurrences were formed by the hydrothermal solutions resulted from Göynükbelen granitoid under the structural control of the fractures observed in the ultramafic rocks. Mineralizations mainly take place at the contact zones between the intrusion and ultramafic rocks. Modal : analyes of the samples from Göynükbelen granitoid were prepared and the results obtained were carried to LE BAS and STRECKEISEN (1991) trianqular diagram which proved that the values for each sample were extending within the area of the diagram for diorite-gabbro, quartz diorite, quartz monzodiorite, tonalite and granodiorite. Here the dominant rock type come out to be tonalite and quartz diorite. A similar result was reached by the application of assay results to De La ROCHE (1980) Ri-R2 diagram. The microscopical study of the samples from diorite- gabro dykes exhibited a subophitic texture. 95 % of these rocks were made of plagio^JLas (An, r t-n) + hornblende. These minerals were escorted by biotite, ~ quartz, alkali feldspar, with accessory minerals (zircon, sphene, apatite) together and some opaque minerals like magnetite, pyrite, calcopyrite. Other rocks of the intrusion appear to have the following mineral association; Plagioclase (An`` <7), quartz + biotite + hornblende + alkali feldspar + accessory minerals like zircon, sphene and apatite together with opaque minerals such as magnetite, i Imeno-magnetite, pyrite, chaleopyrite and rutile. The ratio showing, how much mineral participate wihtin the rock is strictly controlled by the rock type. In general almost all the samples from the intrusion are intensely altered; Plagioclase crystals seem to be epidotized, sericitized and kaolinitized; biotites, chloritized and epidotized; hornblendes, biotitized, chloritized and epidotized while alkali feldsparses are observed being sericitized and kaolinitized. vixiSamples from Göynükbelen intrusion have been analysed for major elements and the results were recalculated using C.I.P.lil. norms. Accordingly quartz, albite, orthoclase and orthoclase, albite, anorthite parameters were shown on triangular diagrams. The results of this work, come out that the governing plagioclase type of the rock was andesine and that the amount of aligoclase and Labradorite taking part in the intrusive rocks were considerably less than andesine. Geochemical major element results also proved that Göynükbelen granitoid intrusion, was derived from a calc-alkali magma. The typical I-type granitoid features, in field setting and petrography are reflected in the major element geochemistry, for example in the alkali-lime relationship which is best displayed in the alkali-lime diagram. The alkali-lime index is 65, thus falling in the calcic subdivision of PEACOCK ' s (1 931 ) classification. Calc-alkaline affinities displayed in the AFM diagram. K`0 vs. Na2D plats based on the criteria of CHAPPELC and WHITE (1974) lie predominantly in the I-type field. In chondrite normalized spider diagram the spectrum of trace elements show smilar trends for granitoids that were developed in island arcs. The LTL (Largeion lithophile) elements (Sr,Ba,Rb, K,Th) and LREE (La) were enriched while the high field strenght elements (Zr,l/lb, Y,Ti) depleted with fractiona tion. These increases and decreases together with rapid fall from K to Nb and rise from Nb to La is most characteristic and in accordance with the trace element distribution of island arc calc alkali magma. With all these chemical characteristics, Göynükbelen granitoids fall into the same compositional fan like I-type and Island arc granitoids (VAG). The VAG character of the Göynükbelen Granitoid is clearly defined on the Rb-SiO` and Rb-(Y + I/lb) discrimination diagrams. In order to determine the arc maturity of the intrusion Rb/Zr-Nb and Rb/Zr-Y diagrams were prepared and on wide range arc maturity between primitive island ar s, continental arcs and normal continental arcs were exhibited. The Paleozoic - Mesozoic metamorphic basement is tectonically overlain by the Upper Cretaceous-Paleocen maf ic-ultramaf ic unit. Dunites and harzburgites cover the widest area within the unit and they both have suffered various amounts of serpentinization however the sieve texture under the microscop is conspicious for both dunites and harzburgites. In the olivine crystals which is main rock forming mineral for ultramafic IXrocks, def ormation lamellae were determined parallel to (1QQ) planes. These deformation lamallae are being interpreted as the result of the deformation mechanism o within the mantle at 1 GDD C and under 5-1 D kb. pressure conditions. MgO, AlpO., and CaD values of ultramafic rocks mere applied to AlpD- - MgG and CaD. -MgD diagrams and the result obtained reflected the fact into that approximately 90 % of the rocks fall into the deplated pirolite area. In AFM diaqram however almost all the mafic and ultramafic rocks took p The Ni-mineralizations originated both to from Göynükbelen granitoid and ultramafic rocks have been studied under two headings: 1- Ni-enrichments developed in red coloured earth zones. 2- Ni-f ormations of hydrothermal origin. Red coloured earth zones were formed by the serpentinization, milonitization, fracturing and alteration of ultramafic rocks in situ and under surfical conditions. With progressing alteration compounds like SiO`, MgO and CaO seem to have left the environment and Fe together with Ni seem to have enriched in a residual manner. Red earth zones are stricktly restricted to the northern, northwestern and Southwestern parts of the area under research, where ultramafic rocks are severaly milonitized and fractured. In these places the width of red earth zones which can only be followed with interruptions and which pinches out at places, changes from few hundred meters to few kilometers. The thicknes of red earth zones which also contain list- waenite blocks and in which several trenches were opened has an average thickness of 3m. Samples from this red earth zones have been collected both in lateral and vertical directions. These sample were thenanalyzed far Ni which showed an irregular distribution. The lowest Ni value obtained is about 1 DD ppm while the highest value does not exceed 9GQ0 ppm. However the average Ni content is 2000 ppm. Idith all these properties those red earth zones hardly resembles the lateritic Fe-Ni deposits and they are also not economical either. Hydrothermal Ni-mineralizations have formed in the central part of the area where the rocks suffered several faulting. Five important Ni-contenting zones were determined in the field and two different types of Ni mineralizations were pinpointed: 1- Hydrothermal Ni-sulfide formations 2- Hydrothermal nickelif erous talc, nickelif erous charitized talc and nickelif erous chlorites. The products of hydrothermal solutions from Göynükbelen granitoid comprise minerals such as chalcopyrite, cubanite and sphalerite as exolution starlets indicate a temperature of 250°C - 300°C (RAMDOHR, 1969) and DO presence of mackinawite 100 C - 150 C, both of which clearly show the temperature of solutions sourced from Göynükbelen granitoid. These solutions must have formed nickel mineralizations following the steps outlined below: 1- Injection of high temperature solutions into ultramafic rocks. 2- Dissolving and remobilizing Ni in ultramafic rocks by hydrothermal solutions. 3- Transportation of Ni to suitable sites. k- Reprecipitation of Ni in the cracks or fractures within ultramafic rocks or substitution of suitable elements (Mg and Fe ) by Ni. Ni-sulphide minerals which have formed in accordance with above processes are pentlandite, heazlewoodite, millerite, mackinawite and by replacement of pentlandite violarite. Awaruite, which is a nickel- iron and asbolane which consisf of Ni and Co escorting the sulfide minerals in small amounts. Almost all the Ni-oxide and sulphide minerals are observed taking place in fractures of serpentinite and serpentinized olivine and pyroxene minerals. Chromite, magnetite, pyrrhotite, pyrite, XIchalcopyrite, cubanite, sphalerite and molibdenite have been observed in association with oxide and sulphide minerals containing Ni. These, oxide and Sulphide minerals altered to second minerals such as goethite, malachite, azurite, maghemite, Fe-Cr-Spinel, tenorite, cuprite, covellite, calcozine, barnite, digenite- neodigenite and delafossite. The second type of nickel mineralizations were formed by substitution °^?Ni carried by hydrothermal solutions essentially Mg and partially Fe in the crystal structures of talc and chlorites. These type of nickel formations are associated with nickel sulfides and other hydrothermal are minerals in the serpentinized dunites and observed as green coloured flakes. Optical properties of these flakes resemble to those of talc and chlorites; x-ray dif f ractiograms overlapp with the refraction peaks of clinoclore and penninite. The electron microprobe analysis of the flakes produced NiD contents between 0.64 % to 42. 9G %. The correlation coefficients between NiO, MgO and Fe`D, as r... M =-0.93, r... p =-0.57, emphasise the fact that Ri was ' y increasing in the flakes against the Mg and Fe contents. The evaluation of electron microprobe results together with the backscattered electron image (BEI) proved a non-homogenous structurally controlled distribution of Ni. As far as reserves are concerned, for the time being hydrothermal nickel formations found in the area under research, seem not to be economical, yet by some additional field work and application of some progressive exploration methods like drilling and trenching, the sound distribution of ore minerals and true reserve can easily be determinad. Xll