黔西南卡林型金矿床与古油藏的成因联系:有机岩相学证据

The genetic relationship between Carlin-type gold deposits and paleo-petroleum reservoirs in SW Guizhou,China:Evidence from organic petrography

黔西南卡林型金矿床中存在两种类型的有机质,一种为具较低反射率的原地藻类体,散布于金矿石和沉积围岩中,多呈层纹状或条带状平行于层理面产出;另一种为热解沥青/焦沥青,多呈微细粒状产于蚀变及矿化岩石中,尤其是高品位矿石中,与主阶段似碧玉状石英、含砷黄铁矿、毒砂紧密共生或伴生,或呈分散的粒状被主阶段和晚阶段的石英、方解石、雄黄等热液矿物包裹。沥青以含较高的与成矿密切相关的微量元素As(4.90%～7.88%)和S(大多为7.48%～15.24%)区别于原地有机质(不含As,S含量2.72%～7.18%)。金矿石热液矿物中常见气相CH4、气液两相CH4-H2O等烃类流体包裹体。古油藏沥青多见于二叠系生物礁碳酸盐岩的溶洞、孔隙、裂缝等开放空间中,或单独产出,或与热液方解石伴生,沥青多呈镶嵌结构,显示出高热演化程度的特点。岩相学证据显示,金矿床成矿流体是一种富含金属和碳氢化合物的油水不混溶的盆地流体,金与烃类有机质一起活化、迁移,并通过不同的沉淀和捕获机制成矿、成藏。

Two principal types of organic matter are present in the Carlin-type gold deposits in SW Guizhou： In situ alginite and hydrothermally migrated bitumen/pyrobitumen. Autochthonous alginite disseminates in both gold ores and host sedimentary rocks and typically appears as lamellae or bands always parallel to bedding planes. Bitumen appears as discrete grains dispersed in altered and mineralized rocks and is particularly prevalent in proximal zones of high grade ores, but is absent in barren sedimentary rocks. In general, bitumen is intimately associated and/or intergrown with the main stage jasperoidal quartz patches, arsenian pyrite, and arsenopyrite. It also occurs as discrete grains enclosed by the main and late stage quartz, calcite and realgar. Bitumen in gold ores has higher contents of ore-associated trace elements As （4. 90%- 7. 88%） and S （typically 7. 48%- 15.24%）, compared to autochthonous alginite with negligible As and lower S concentrations （2. 72%- 7.18%）. Hydrocarbon fluid inclusions, ranging from those filled only by vapor hydrocarbons （CHI） to inclusions consisting of a vapor hydrocarbon phase （CH4） and an aqueous liquid phase, are common in hydrothermal minerals. Bitumen in paleo petroleum reservoirs is commonly observed filling open spaces （pores and fractures） in Permian reef carbonate rocks, occurring either alone or associated with calcite. It commonly shows fine mosaic texture, suggesting a high thermal maturity. Organic petrographic evidence suggests that gold originated and migrated along with the hydrocarbons in an immiscible, ore-and hydrocarbon-bearing, basinal fluid system. The gold mineralization and hydrocarbon accumulation took place by different depositional and trapping mechanisms.