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首页> 外文期刊>Mineralium Deposita >Archaean lode gold mineralisation in banded iron formation at the Kalahari Goldridge deposit, Kraaipan Greenstone Belt, South Africa
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Archaean lode gold mineralisation in banded iron formation at the Kalahari Goldridge deposit, Kraaipan Greenstone Belt, South Africa

机译：南非Kraaipan绿石带卡拉哈里金岭矿床带状铁形成中的古生铁矿金矿化

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摘要

The Kalahari Goldridge Mine is located within the Archaean Kraaipan Greenstone Belt, about 60 km southwest of Mafikeng in the North West Province, South Africa. The ore body thickness varies from 15 to 45 m along a strike length of about 1.5 km within approximately N–S striking banded iron formation (BIF). The stratabound ore body is hosted primarily by BIF, which consists of alternating chert and magnetite–chlorite–stilpnomelane–sulphide–carbonate bands of millimetre- to centimetre scale. A footwall of sericite–carbonate–chlorite schist underlain by mafic amphibolite occurs to the west and carbonaceous metapelites in the hanging wall to the east. Overlying the hanging wall, carbonaceous metapelites, units of coarse-grained metagreywackes fining upwards, become increasingly conglomeratic up the stratigraphy. Small-scale isoclinal folds, brecciation, extension fractures and boudinage of cherty BIF units reflect brittle-ductile deformation. Fold axial planes have foliation, with subvertical plunges parallel to prominent rodding and mineral lineation in the footwall rocks. Gold mineralisation is associated with two generations of quartz–carbonate veins, dipping approximately 20° to 40° W. The first generation consists of ladder-vein sets (group IIA) preferentially developed in centimetre-scale Fe-rich mesobands, whereas the second generation consists of large quartz–carbonate veins (group IIB), which locally crosscut the entire ore body and extend into the footwall and hanging wall. The ore body is controlled by mesoscale isoclinal folds approximately 67° E, orthogonal to the plane of mineralised, gently dipping veins, defining the principal stretching direction and development of fluid-focussing conduits. The intersections of the mineralised veins and foliation planes of the host rock plunges approximately 08° to the north. Pervasive hydrothermal alteration is characterised by chloritisation, carbonatisation, sulphidation and K-metasomatism. Gold is closely associated with sulphides, mainly pyrite and pyrrhotite, and to a lesser extent, with bismuth tellurides and carbonate minerals. Mass balance transfer calculations indicate that hydrothermal alteration of BIF involved enrichment of Au, Ag, Bi, Te, S and CO2 (LOI), MgO, Ba, K and Rb, but significant depletion of SiO2 and, to a lesser extent, Fe2O3. Extensive replacement of magnetite and chlorite in BIF and other pelitic sedimentary rocks by sulphide and carbonate minerals, both on mesoscopic and microscopic scales, is evidence of interaction of CO2- and H2S-bearing fluids with the Fe-rich host rocks. The fineness of gold grains ranges from 823 to 921, similar to that of other epigenetic Archaean BIF-hosted gold deposits, worldwide.
机译：Kalahari Goldridge矿位于南非西北省Mafikeng西南约60公里的Archaean Kraaipan Greenstone带内。矿体厚度在大约N–S冲击带状铁矿层（BIF）内，沿着走向长度约1.5 km，变化范围为15至45 m。地层约束的矿体主要由BIF托管，BIF由毫米级至厘米级的交替的cher石和磁铁矿-亚氯酸盐-lp石mel烷-硫化物-碳酸盐带组成。镁铁质角闪岩衬托下的绢云母－碳酸盐－亚氯酸盐片岩的下盘壁出现在西部，而含碳的变质岩发生在东部的悬挂壁中。上悬壁上的碳质变质岩，向上粗化的粗粒状变质灰岩单元在地层上越来越聚结。珍贵的BIF单位的小范围等轴折痕，角状瘤，延伸性骨折和胸腔反映了脆性-韧性变形。折叠的轴向平面具有叶状结构，其下垂突平行于下盘壁岩石中的突出的杆ding和矿物线。金矿化与两代石英碳酸盐岩脉相关，倾角约20°至40°W。第一代由梯形脉组（IIA组）组成，优先在厘米级富铁介带中发育，而第二代由大的石英-碳酸盐脉（IIB组）组成，局部横切整个矿体，并延伸到下盘壁和上盘壁。矿体受中尺度等时线折线控制，折线约67°E，垂直于矿化的，缓和的矿脉平面，定义了主要的拉伸方向和流体聚焦导管的发育。矿化脉和主岩的叶面的相交点向北倾斜约08°。普遍的热液蚀变的特征是氯化作用，碳酸盐化作用，硫化作用和钾致突变作用。金与硫化物紧密相关，主要是黄铁矿和黄铁矿，在较小程度上与碲化铋和碳酸盐矿物相关。质量平衡转移计算表明，BIF的水热蚀变涉及金，银，铋，碲，硫和二氧化碳（LOI），MgO，Ba，K和Rb的富集，但SiO2和，在较小程度上是Fe2 O3 。在介观和微观尺度上，硫化物和碳酸盐矿物广泛替代了BIF和其他胶质沉积岩中的磁铁矿和绿泥石，证明了含CO2和H2S的流体与铁的相互作用。丰富的寄主岩石。金粒的细度介于823至921之间，与全球其他表观成因的古生化BIF托管的金矿床相似。

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