铜官山矿田铜金成矿模式探讨

A Tentative Discussion on the Copper and Gold Metallogenic Model of the Tongguanshan Orefield

铜官山矿田是长江中下游铜铁金成矿带铜陵矿集区中4个主要矿田之一,矿田由铜官山铜矿床、天马山硫金矿床、金口岭铜金矿床组成。矿田内地表出露志留系至三叠系地层,岩体有铜官山石英闪长岩、天鹅抱蛋山石英闪长岩和金口岭花岗闪长岩等。根据矿体产状、矿化特征、蚀变类型等,矿体分为夕卡岩型矿体、层状矿体及细脉浸染型矿体。不同产状矿体是由不同容矿构造所决定的,夕卡岩型矿体是由接触带构造控制的,层状矿体是由C2+3/D3ω层间滑脱面构造控制的,当两种构造交叉时形成“人”形或“Y”形矿体。层状矿体的形成经历了2个成矿阶段,即燕山期岩浆作用形成的含铜金等成矿物质的岩浆热液,沿着层间构造移动时,交代叠加改造在晚石炭世沉积形成的含铜等的黄铁矿层,形成层状铜硫矿体或硫金矿体。Pb、O等同位素特征及成矿温度研究资料表明,成矿物质和含矿热液主要来源于岩浆,部分来源于地层。由于区域基底控岩断裂构造活动的多期性、长期性及脉动性,从而导致岩浆房的演化、分异,不仅使岩性上存在一定差异,而且不同岩体其含铜、金性上有一定差异。不同矿种是由于不同期次岩浆含铜金性不同所决定的。

Being one of the four main orefields in the Tongling ore concentration area along the Middle and Lower Yangtze Valley copper-iron-gold metallogenic belt, the Tongguanshan orefield consists of the Tongguanshan copper deposit, the Tianmashan sulfur-gold deposit and the Jinkouling copper-gold deposit. In the orefield, Silurian to Triassic strata are exposed at the surface, and the in-trusives include the Tongguanshan quartz diorite, the Tianebaodanshan quartz diorite and the Jinkouling granodiorite. According to attitudes of the orebodies, characteristics of mineralizations and types of alterations, the orebodies can be classified into skarn orebodies, stratiform orebodies and veinlet disseminated orebodies. Orebodies of different attitudes are decided by different host structures: skarn orebodies are controlled by structures of the contact zone, stratiform orebodies are governed by C2 + 3/D3w interωlayer detachment surface structures, and where these two kinds of structures are intersected with each other, the (shaped or Y-shaped orebodies are formed. The formation of the stratiform orebodies experienced two ore-forming stages, i. e. , when the copper-, gold-bearing magmatic hydrothermal fluids formed by Yanshanian magmatic activity moved along the interlayer structures, they replaced, superimposed upon and reformed the copper-bearing pyrite bed formed by Late Carboniferous sedimentation and thus yielded stratiform copper-sulfur orebodies or sulfur-copper orebodies. Studies of lead and oxygen isotope data and ore-forming temperatures show that the ore-forming materials and ore-bearing hydrothermal fluids were derived mainly from magma and partly from strata. The multi-phase and protracted natures as well as pulsation of the activities of the regional basement rock-controlling fractural structures led to the evolution and differentiation of the magma chamber and, as a result, there exist differences not only in petrologic characters but also in copper and gold potentials of the intrusive bodies. Different ore species are attributed to different copper and gold potentials at different magmatic stages.