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首页> 外文期刊>Mineralium deposita >Pressure, temperature, and timing of mineralization of the sedimentary rock-hosted orogenic gold deposit at Klipwal, southeastern Kaapvaal Craton, South Africa
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Pressure, temperature, and timing of mineralization of the sedimentary rock-hosted orogenic gold deposit at Klipwal, southeastern Kaapvaal Craton, South Africa

机译：南非Kaapvaal Craton东南部Klipwal沉积岩造山造金矿床的压力，温度和矿化时间

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摘要

Gold mineralization in the Klipwal Shear Zone (KSZ) at the Klipwal Gold Mine is confined to laminated quartz-carbonate lodes, stringers, and associated alteration in sandstone and siltstone of the Delfkom Formation in the upper Mozaan Group of the Mesoarchaean Pongola Supergroup. The moderately dipping brittle-ductile KSZ strikes N-S with an oblique-reverse, sinistral sense of shear. The deformational events that are recognized include an early compressional phase that produced anastomosing shears defined by shear fabrics with numerous shear-parallel laminated quartz-carbonate fault-fill veins and, in places, extensional quartz vein stockworks, and a late brittle reactivation phase that produced fault breccias, displacing earlier extensional veins. Three closely spaced economic reefs (lodes) are developed: the main R-reef constitutes the KSZ, while the J- and H-reefs represent footwall splays. Alteration comprises chlorite, muscovite, epidote, feldspar, and carbonates along with pyrite, arsenopyrite, and chalcopyrite +/- pyrrhotite. An inner alteration zone is dominated by laminated quartz-carbonate veins with alternating quartz-carbonate-rich and muscovite-chlorite-rich laminae, whereas the proximal zone is characterized by alteration halos of K-feldspar, albite, epidote, chlorite, and muscovite along with carbonates and associated quartz veins. Chlorite thermometry from the inner and proximal zones yielded temperatures of 267 to 312 A degrees C. Arsenopyrite compositions provide temperatures in the same range, 255 to 318 A degrees C. Fluid inclusion microthermometry and Raman spectrometry of quartz veins in the mineralized reefs reveal the presence of metamorphogenic aqueous-gaseous fluid with an average salinity of 6.5 wt% NaCl equiv. Fluid compositions and estimated pressure-temperature (P-T) range (1.1 to 2.5 kbar at 255 to 318 A degrees C) are typical of orogenic gold deposits. Devolatilization during the regional facies metamorphism of the Pongola Supergroup is considered the likely fluid-forming event with fluid flow focused into a "compressional jog" of the KSZ. Shear-induced pressure fluctuations generated a phase separation of the initial aqueous-gaseous fluid, producing a gaseous and low-salinity aqueous fluid. This, together with fluid-rock interaction, and a decrease in fO(2) lead to sulfide and gold precipitation at Klipwal. Re-Os data from six sulfide samples constrain the age of sulfide precipitation and, by inference, gold mineralization, to 2563 A +/- 84 Ma, with an initial Os-187/Os-188 = 0.29 A +/- 0.08 (MSWD = 0.38). This age is distinctly younger than the post-Pongola granites (2863-2721 Ma), ruling out the association of granite emplacement with mineralization. This would suggest that mineralization is linked to the regional D-3 folding event which reactivated the KSZ after emplacement of the post-Pongola granites and that final brittle, post-mineralization reactivation is related to Karoo age faulting. Low initial Os values suggest that ore fluid interacted with mafic rocks, leaching non-radiogenic Os, the likely source being the deeper seated Nsuze Group volcanics and/or the greenstone belts that underlie the Pongola Supergroup.
机译：Klipwal金矿的Klipwal剪切带（KSZ）中的金矿化作用仅限于Mesoarchaean Pongola超群上Mozaan组上部Delfkom组砂岩和粉砂岩的层状石英碳酸盐矿，桁条以及相关的蚀变。中等倾倒的脆性延性KSZ以斜向，反正弦的剪切力撞击N-S。公认的变形事件包括早期的压缩阶段，该阶段产生的吻合剪切是由剪切织物定义的，该剪切织物具有大量平行剪切的叠层石英-碳酸盐岩断层充填脉，局部还存在伸展的石英脉储层，最后产生了脆性复活阶段。断裂角砾岩，移位较早的延伸静脉。形成了三个紧密间隔的经济礁（成礁）：主要的R礁构成KSZ，而J礁和H礁则代表下盘张开。蚀变包括绿泥石，白云母，附子，长石和碳酸盐以及黄铁矿，毒砂和黄铜矿+/-黄铁矿。内部蚀变带以层状石英-碳酸盐脉为主，富含石英-碳酸盐和白云母-亚氯酸盐交替层状，而近端带的特征是钾长石，钠长石，埃奇狄德，绿泥石和白云母沿碳酸盐和相关的石英脉。内部和近端区域的亚氯酸盐温度计产生的温度为267至312 A摄氏度。毒砂组成的温度范围为255至318A。矿物包裹体中石英脉的流体包裹体微热法和拉曼光谱表明存在平均盐度为6.5 wt％NaCl的变态含水气体流体。流体成分和估计的压力-温度（P-T）范围（255至318 A摄氏度下为1.1至2.5 kbar）是造山型金矿的典型特征。 Pongola超群的区域相变质作用期间的脱挥发分被认为是可能的流体形成事件，其中流体流集中在KSZ的“压缩点动”中。剪切引起的压力波动产生了初始含水气态流体的相分离，从而产生了气态和低盐度的含水流体。这连同流体-岩石相互作用，以及fO（2）的下降导致Klipwal处的硫化物和金沉淀。来自六个硫化物样品的Re-Os数据将硫化物沉淀的年龄以及通过推断推断的金矿化作用限制在2563 A +/- 84 Ma，初始Os-187 / Os-188 = 0.29 A +/- 0.08（MSWD = 0.38）。这个年龄明显比蓬戈拉后的花岗岩（2863-2721 Ma）年轻，排除了花岗岩侵位与矿化的联系。这表明矿化与区域性D-3折叠事件有关，该事件在庞戈拉后花岗岩埋入后重新激活了KSZ，而最终的脆性，矿化后重新激活与Karoo年龄断层有关。低的初始Os值表明矿石流体与铁镁质岩相互作用，浸出非放射性的Os，可能的来源是位于Pongola超群之下的Nsuze组火山岩和/或绿岩带。

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