周至马鞍桥金矿床成矿控制条件及找矿标志

马鞍桥金矿床是产于南秦岭泥盆系中的大型微细浸染型金矿，沉积—叠加改造成矿特征典型。矿体沿上泥盆统上部层位稳定分布，多与围岩整合产出。矿石类型有破碎蚀变岩型、蚀变千枚岩型、炭质片岩型和含金石英脉型。矿石构造有浸染状、细脉浸染状、细脉状和角砾状。矿物成分主要为黄铁矿、磁黄铁矿和石英、绢云母等，金主要呈显微金、超显微金分布于矿物粒间或被吸附于矿物表面。矿床由多种地质作用经过多期多阶段形成，主要受构造、沉积地层和岩浆活动控制。区域性大型韧性剪切带控制金矿带、金矿区的展布，地区性二级脆性断裂控制金矿床的范围，局部的更次级层间破碎带、断裂裂隙带控制矿体的就位。含了地层为矿床形成提供了主要的成矿物质。岩浆活动为形成合矿流体提供了热源并是热液运移的主要热动力。

THE ORE-FORMING CONDITION AND ORE-HUNDING INDICATORS OF MA'ANQIAO GOLD DEPOSIT IN ZHOUZHI, XI'AN

Ma'anqiao gold deposit, which is situated in the Devonian System of the Southern Qinling Ranges,is a large micro-grained disseminated ore deposit characterized by the metallogenic features of sedimentationand imposed reformation. The ore bodies are steadily located, most in concordance, in the upper part of theUpper Devonian. The ores are rubble altered type, altered phyllite type, carbonaceous schist type and gold.bearing quartz vein type. The ore textures are disseminated, veinlet disseminated, veinlet and breccia type.The minerals are mainly pyrite, pyrrhotite, quartz, sericite and so on. The gold is micro-type and ultramicrotype distributed in the major minerals or absorpted by the mineral surfaces. The ore deposit is formed by multiple geological activities of multistages and multiphases. And the major controlling factors are structure, sedimentary strata and magmatic activities. The regionnal large ductile sheer belt controls the distribution of theore zone or are field, the secondary brittle faults control the range of the ore deposit and the local interlagerfracture zone and faults fracture control the sites of the ore bodies. The ore-bearing strata are the majorsources of the ore-forming material. And the magmatic activities provided the thermal source needed for themigration of the ore-bearing fluids.