新疆玉海－三岔口铜矿黑云母矿物化学特征及成岩成矿意义
Petrogenesis and Mineralization of Yuhai and Sanchakou Copper Deposit:Constraints from Mineral Chemistry of Biotite in Xinjiang,Northwestern China

黑云母的化学成分对于揭示结晶条件、岩石成因、成矿演化以及含矿性评价等具有重要的指示意义.利用电子探针(EPMA)对新疆玉海和三岔口铜矿中的黑云母进行成分分析，结果表明与成矿相关岩体的黑云母具有富镁贫铁的特征，而无矿化岩体中的黑云母则呈现富铁贫镁的特征.分析结果显示矿化岩体中黑云母为再平衡镁质黑云母，而无矿化岩体中黑云母为原生铁质黑云母；它们的寄主岩石均属于I型花岗岩，形成于与俯冲相关的构造背景，但是与矿化相关岩体的岩浆源区为壳幔混合来源，而无矿岩体的源区为地壳来源，形成过程中有新生地壳组分的混染；两类黑云母的结晶温度为529～677 ℃，寄主岩体的固结压力为1.1～2.8 kbar，均形成于高氧逸度条件；此外，黑云母的Mg/Fe和Fe2+/(Fe2++Mg2+)还可以区分斑岩型铜矿的含矿性.
Mineral composition of biotite is a significant indicator of revealing the crystallization conditions, petrogenesis, mineralization and evaluation of orebearing potential in porphyry copper deposit systems. This study utilizes electron microprobe analyses (EPMA) to determine the mineral composition of biotite in Yuhai and Sanchakou porphyry copper deposits, Xinjiang. The EPMA data shows that the characteristics of biotite are rich in magnesium and poor in iron in orebearing intrusions; whereas those in orebarren intrusions are rich in iron and poor in magnesium. The biotite is mainly composed of reequilibrated Mgbiotite in orebearing intrusions and is primary Febiotite in orebarren intrusions. The host rocks of all the biotite are Itype granite and are formed during subduction. The orebearing magma was derived from the mixing of mantle and crust, however, the orebarren magma was mainly generated from crust with involvement of juvenile crustal components during formation. The crystallization temperature and pressure of biotites are 529-677℃ and 1.1-2.8kbar, and they formed in the condition of high oxygen fugacity. In addition, the Mg/Fe and Fe2+/(Fe2++Mg2+) of biotites may be used as a tool to discriminate between the orebearing and orebarren intrusions in porphyry copper systems