Extreme variation of sulfur isotopic compositions in pyrite from the Qiuling sediment-hosted gold deposit, West Qinling orogen, central China: an in situ SIMS study with implications for the source of sulfur
Extreme variation of sulfur isotopic compositions in pyrite from the Qiuling sediment-hosted gold deposit, West Qinling orogen, central China: an in situ SIMS study with implications for the source of sulfur
复制标题
中国中部西秦岭造山带秋岭沉积金矿床黄铁矿中硫同位素组成的极端变化：原位 SIMS 研究及其对硫来源的影响
DOI：
10.1007/s00126-015-0597-9
复制
发表时间：
2015-08-01
影响因子：
4.8
通讯作者：
Koenig, Alan E.
中科院分区：
文献类型：
--
作者：
Chen, Lei;Li, Xian-hua;Koenig, Alan E.
利用高空间分辨结构（扫描电镜）、化学（电子探针）、激光烧蚀-电感耦合等离子体质谱（LA-ICP-MS）和硫同位素(次级离子质谱（SIMS）分析方法，对西秦岭造山带丘岭沉积物金矿床（232±4 Ma）黄铁矿进行了分类，探讨了热液流体中硫的来源和演化规律。结果表明，3个共生期黄铁矿的硫同位素组成差异较大（−27.1 ~ +69.6‰）。矿前树状黄铁矿的δ34S值为负- 27.1 ~ - 7.6‰，具有As、Au、Cu、Co、Ni等低浓度特征，是该区古生代碳酸盐岩和碎屑层序沉积和成岩过程中海相硫酸盐的细菌还原作用，是该区主要岩性，也是整个西秦岭造山带众多沉积型金矿床的主要寄主。矿期热液黄铁矿具有较高的Au、As、Cu、Sb、Tl、Bi等元素，δ34S正值范围较窄，为+8.1 ~ +15.2‰。硫同位素数据与西秦岭造山带许多三叠纪造山带金矿床和古生代沉积喷发型铅锌矿床的矿石黄铁矿相当，均主要赋存于泥盆系层序。这种相似性表明，秋岭含金黄铁矿的硫主要来源于古生代海相沉积岩的变质脱挥发作用。矿石期后黄铁矿δ34S值异常高，δ34S值介于+37.4 ~ +69.6‰之间，是由下伏寒武系高δ34S的沉积岩中蒸发岩硫酸盐热化学还原所致。单矿期黄铁矿中Au含量和硫同位素组成的变化可能反映了低δ34S值的原生地下水被高δ34S值的含金变质流体所取代。成矿岩的极低变质作用和黄铁矿中硫的变质衍生作用表明，秋岭金矿床是西秦岭造山带造山带金系统的层向表现。
High spatial resolution textural (scanning electron microscope (SEM)), chemical (electron microprobe (EMP)) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS)), and sulfur isotopic (secondary ion mass spectrometry (SIMS)) analyses of pyrite from the Qiuling sediment-hosted gold deposit (232 ± 4 Ma) in the West Qinling orogen, central China were conducted to distinguish pyrite types and gain insights into the source and evolution of sulfur in hydrothermal fluids. The results reveal an enormous variation (−27.1 to +69.6 ‰) in sulfur isotopic composition of pyrite deposited during three paragenetic stages. Pre-ore framboidal pyrite, which is characterized by low concentrations of As, Au, Cu, Co, and Ni, has negative δ34S values of −27.1 to −7.6 ‰ that are interpreted in terms of bacterial reduction of marine sulfate during sedimentation and diagenesis of the Paleozoic carbonate and clastic sequences, the predominant lithologies in the deposit area, and the most important hosts of many sediment-hosted gold deposits throughout the West Qinling orogen. The ore-stage hydrothermal pyrite contains high concentrations of Au, As, Cu, Sb, Tl, and Bi and has a relatively narrow range of positive δ34S values ranging from +8.1 to +15.2 ‰. The sulfur isotope data are comparable to those of ore pyrite from many Triassic orogenic gold deposits and Paleozoic sedimentary exhalative (SEDEX) Pb-Zn deposits in the West Qinling orogen, both being hosted mainly in the Devonian sequence. This similarity indicates that sulfur, responsible for the auriferous pyrite at Qiuling, was largely derived from the metamorphic devolatization of Paleozoic marine sedimentary rocks. Post-ore-stage pyrite, which is significantly enriched in Co and Ni but depleted in Au and As, has unusually high δ34S values ranging from +37.4 to +69.6 ‰, that are interpreted to result from thermochemical reduction of evaporite sulfates in underlying Cambrian sedimentary rocks with very high δ34S values. The variations in Au content and sulfur isotopic compositions across a single ore-stage pyrite grain may reflect displacement of indigenous groundwater with low δ34S values by auriferous metamorphic fluids with high δ34S values. The very low-grade metamorphism of the host rocks and the metamorphic derivation of sulfur for the ore pyrite indicate that the Qiuling sediment-hosted gold deposit is an epizonal manifestation of an orogenic gold system in the West Qinling orogen.