岩浆因素对中国东部铜陵矿集区差异性矿化的控制作用:来自角闪石、斜长石矿物学证据

The controlling role of magmatic factors on the differential mineralization in the Tongling ore district,eastern China:Evidence from the mineralogy of amphibole and plagioclase

冬瓜山铜(金)矿床和新桥硫铁铜金矿床是铜陵矿集区内两个大型夕卡岩型矿床,二者成矿地质背景相似,矿体产于同一地层层位,冬瓜山矿床以黄铜矿和磁黄铁矿为主,新桥矿床以黄铁矿和磁铁矿为主,二者矿物组合差异性非常明显,但造成二者矿物组合差异的关键控制因素还不清楚。针对这一科学问题,本文以二者成矿岩体中的角闪石和斜长石为研究对象,拟揭示岩浆因素对二者差异性矿化的控制作用。冬瓜山矿床青山脚石英二长闪长岩和新桥矿床矶头石英闪长岩角闪石和斜长石岩相学和电子探针(EPMA)主量元素和LA-ICP-MS微量元素分析结果显示,青山脚岩体中的角闪石大部分属于镁角闪石系列;矶头岩体中的角闪石大部分属于镁角闪石和浅闪石系列。青山脚岩体和矶头岩体的角闪石结晶压力、结晶温度、结晶深度、氧逸度和含水量分别为41~306 MPa和23~225 MPa,691~916℃和634~918℃,1.6~11.6 km和0.9~8.5 km,ΔNNO=0~2.3和ΔNNO=-0.4~2.4,3.7%~5.5%和3.1%~5.4%,青山脚和矶头岩体内角闪石以地壳型为主,少部分为壳幔混合型。两个岩体中斜长石多为中长石,根据斜长石结构和成分剖面特征,推测青山脚和矶头岩体晶体群分别来自5个和4个不同的岩浆子系统,都经历了镁铁质岩浆的注入和混合作用。我们认为镁铁质岩浆中氧逸度和元素含量的差异控制了冬瓜山和新桥的差异性矿化。

The Dongguashan Cu(Au)deposit and the Xinqiao S-Fe-Cu-Au deposit are two large skarn-type deposits in the Tongling Ore District.These deposits share a similar metallogenic geological background and are located in the same stratigraphic horizon.However,they exhibit distinct differences in mineral assemblages with the Dongguashan deposit being dominated by chalcopyrite and pyrrhotite,while the Xinqiao deposit is characterized by pyrite and magnetite dominance.The factors influencing these contrasting mineral assemblages remain unclear.To address this scientific question,this study focuses on amphibole and plagioclase in the ore-forming rock masses of both deposits to investigate the magmatic influences on their differential mineralization.Petrographic analysis,EPMA major element analysis,and LA-ICP-MS trace element analysis were conducted on amphibole and plagioclase from the Qingshanjiao quartz monzodiorite of the Dongguashan deposit and the Jitou quartz diorite of the Xinqiao deposit.The results reveal that most amphiboles in the Qingshanjiao rock mass belong to the magnesium amphibole series,whereas those in the Jitou rock mass belong to both the magnesium amphibole and amphibole series.The crystallization pressure,crystallization temperature,crystallization depth,oxygen fugacity and water content of amphibole in the Qingshanjiao and Jitou intrusions are 41306 MPa and 23225 MPa,691916℃and 634918℃,1.611.6 km and 0.98.5 km,ΔNNO=02.3 andΔNNO=-0.42.4,3.7%5.5%and 3.1%5.4%,respectively.The amphiboles in both intrusions are predominantly of crustal origin,with some showing characteristics of crust-mantle mixing.Plagioclase in both rock masses is predominantly feldspar.Based on the structure and composition profile of plagioclase,it is suggested that the crystal groups in the Qingshanjiao and Jitou rock masses originate from five and four different magma subsystems,respectively,and have undergone mafic magma injection and mixing.The study proposes that variations in oxygen fugacity and element content in mafic magmas play a key role in controlling the differential mineralization observed in the Dongguashan and Xinqiao deposits.