湖南符竹溪金矿床多因复成模式及其找矿意义

符竹溪金矿床的形成,历经长期多阶段成矿演化,具有典型的多因复成模式特征,既具多阶段多来源多成因复合叠加成矿特点,又有主阶段主来源主成因成矿特色。主成矿作用为中低温热液成因,成矿热液和驱动力是中生代地洼阶段构造-岩浆活化作用,与脆-韧性剪切带及花岗斑岩的活动有密切时空联系,从而得出四阶段多因复成的成矿模式。据此成矿模式找矿和成矿预测,获得显著的找矿效果。在矿区深部,边部和外围找到了新矿体,扩大了矿床规模,解除了矿山资源危机。

POLYGENETIC COMPOUND MODEL FOR THE FUZHUXI GOLD DEPOSIT OF HUNAN PROVINCE AND ITS PROSPECTING

The Fuzhuxi gold deposit is located in the southern part of Anhua-Taojiang East-West trending subbelt of the northcastern part of Xuefengshan upwarping belt. The deposit belongs to the Taojiang geodome of the northeastern part of the geodome system of the Jiangnan Diwa region. The gold-bearing strata occur within the Proterozoic Lenjiaxi Group and Madiyi Formation of Banxi Group. The ore-bearing wall rocks are the thick clasticargillaceous siltstone and slate which belong to the neritic flysch formation. Gold concentratings contained in the gold-bearing strata is 10-15 g/t, and antimony 25-27 g/t.Linear high fractures are very developing in the deposit. The cast west and northwestern-trending fractures are the best developed and exert the greatest control upon the ore, whereas the northeastern and north—south trending fractures are less pronounced, and exeert only a secondary control upon the ore's accumulation. The wall rocks proximal to the orebodies have undergone intense contact metamorphism and consequently exhibit silicification, pyritization, sericitization, chloritization, and schistosity. The ore-controlling fractures are characteristic of a ductile—brittle shear—plane zone. The economic gold mineralization represent formation in the late stage of the ductile-brittle shear-plane zone with the antimony mineralization occuring in the last stage.The Fuzhuxi deposit belongs to the Au-Sb quartz, fracture zone type with As ore breccia and fragments. The main economic mincrals are gold, antimonite, and pyrite. The ore is characterized by the assemblage or Au, Sb, As, Mo and Hg. The As association suggests an indicator element for prospecting. The zonation is vertical and in descending order one has: an altered bleached zone, a silicified zone, a quartz veinlet zone, a gold-antimony-bearing quartz fracture zone, an antimony-gold-bearing quartz fracture zone, a gold-bearing (no antimony) quartz fracture zone, and polymetal-bearing mineralized zone. The total zone of mineralization extends up to 1000 m vertically.The formation of the antimony-gold deposit has undergone long-term multistage evolution, characterized by both typical polygenetic and compound mineralization but also a main-stage, single-source, enrichment mineralization. The metallogenic temperature of the major mineralization was 235-207℃ and the metallogenic pressure was estimated to be 815-760 bars. The hydrothemal ore-forming source and power are form the tectono-magmatic activation during the Mesozoic Diwa stage, and are further related to both the ductile-brittle shear-plane zone and to the granite-porphyry in space and time. Therefore, the four-stage polygenetic and compound metallogenic model are: (1) The middle-late Proterozoic (1400-800 Ma) sedimentation-diagenesis and original enrichment stage, (2) The Xuefengnian (800-700 Ma) metamorphism and pre-enrichment stage, followed by the incipient formation of the deep gold-bearing ductile shear-plane zone. (3) Indosinian-early Yanshanian (210-140(?) Ma) tectono-magmatic activation and gold metallogenic stage, followed by the intrusion of gabbro-diabase and granite dikes, (The isotopic age of the intrusion is 209 Ma which dates the activation of the gold-bearing ductile shear-plane zones and the formation of hydrothermal genetic gold-bearing quartz veins.) (4) The late Yanshanian Sb-Au metallogenic stage, the gold-bearing ductile shear-plane zones were reactivated and were transformed into the brittle fractures. (Consequently, a large amount of antimonite filled in the upper of the quartz fracture zones and superimposed on the previous gold-bearing quartz veins.)From pursuing the polygenetic compound Diwa model, new ore bodies have extended the deposits and resolving resource crisis of the gold mine.