甘肃小柳沟式钨钼矿床成矿模式探讨

小柳沟钨钼多金属矿床位于北祁连加里东造山带西段。通过研究小柳沟矿集区典型矿床地质背景及矿床地球化学特征,认为矿床的产出受地层、构造和岩浆岩等因素的综合控制。成矿物质W主要来自地层,部分来自岩浆,岩浆作用的热动力驱动、虹吸作用及流体交代作用是W进入岩浆的主要原因; Mo主要来自壳内S型花岗岩,同时受到深部岩浆的供应;硫主要来自岩浆热液,在近地表石英硫化物阶段硫可能受到地层或地壳重熔花岗岩和大气地表水中硫的混合作用;成矿流体主要来自岩浆热液,在晚期有大气降水的混合。矿床成矿年龄集中在392～428 Ma之间,二长花岗岩成岩年龄为454 Ma左右,花岗闪长岩形成时代为418 Ma左右,二长花岗岩成岩与矿体成矿时差相差40 Ma左右,该时差超过一般岩体冷却所需要的时间,结合构造演化认为成矿与挤压向伸展转换阶段的构造减压密切相关,有部分成矿年龄落入海西期和燕山期,认为成矿后期经历了海西期和燕山期岩浆热事件的改造。根据矿床成因建立了小柳沟矿集区成矿模式,并对进一步找矿方向提出了建议。

Discussion on the Metallogenic Model of the Xiaoliugou W-Mo Deposit in Gansu

Xiaoliugou W-Mo polymetallic deposit is located in Caledonian orogenic belt on the west part of the Northern Qilian Mountains. Through in-depth study on the geological setting and geochemical characteristics in Xiaoliugou ore-gathering Area, it is concluded that that the output of deposit is integratedly controled by the stratigraphy, tectonics and igneous rocks.The ore-forming materials of W are derived mainly from the formation; part of it comes from the magma. Thermal power drive from magmatism, siphon action and fluid metasomatism are the main reasons for W to enter the magm.Mo mainly comes from S-type granites in crust and is supplied by deep magma. Sulfur mainly from magmatic hydrothermal, and sulfur may be mixed by formations, crust remelting granite or atmospheric surface water in the quartz sulfide phase in the near surface.The ore-forming fluids mainly came from magmatic hydrothermal and were mixed by atmospheric precipitation in the late stage. The mineralization age of Xiaoliugou W-Mo polymetallic deposit is between 392 Ma and 428 Ma, and age of adamellite and granodiorite is about 454 Ma and of granodiorite formed is about 418 Ma. The time difference is longer that the time required for cooling of rock. Combined with the tectonic evolution, it is inferred that metallogeny is closely related to the decompression in conversion stage from extrusion to stretch of the structure.At the same time, some metallogenic ages fall into Hercynian and Yanshanian, so it is believed that metallogeny have experienced transformation caused by the magmatic heat events in Hercynian and Yanshanian. Finally, according to the genesis of deposit, the paper established a metallogenic model for Xiaoliugou ore-gathering area, and made recommendations for further prospecting direction.