西藏嘎拉勒铜金矿床地质特征与控矿条件分析

嘎拉勒铜金矿床位于冈底斯成矿带西段北缘,是近年来该区域发现的一个重要的典型镁质矽卡岩型铜金矿床。本文在矿区大比例尺地质填图基础上,结合前人研究资料,对该矿床地质特征和控矿条件进行了系统阐述和分析。矿区内出露地层主要为下白垩统捷嘎组白云岩和白云质灰岩,其下伏为下白垩统郎久组砂岩、粉砂岩和流纹质-英安质火山岩及火山碎屑岩。矿区内至少发生了3期构造变形,第1期形成北西向褶皱和北东向张性横断层,第2期形成北东向褶皱、北东向压性纵断层和北西向小型张性横断层,第3期形成近南北向正断层。区内自早到晚侵入有燕山晚期斑状石英闪长岩、闪长玢岩、石英闪长岩、花岗闪长岩和花岗斑岩。在石英闪长岩和花岗闪长岩与捷嘎组白云岩和白云质灰岩接触带附近形成典型镁质矽卡岩,包括早、晚两个阶段,早阶段形成由橄榄石、粒硅镁石和少量尖晶石、石榴子石、透辉石组成的干矽卡岩,晚阶段形成由蛇纹石、金云母和少量绿帘石组成的湿矽卡岩,叠加在干矽卡岩之上或其外侧,构成自岩体向外的橄榄石+尖晶石+粒硅镁石±石榴石±金云母带、金云母+蛇纹石±橄榄石±石榴石±透辉石带、蛇纹石+金云母+绿帘石±透辉石带、蛇纹石±金云母化大理岩带。矿体呈层状、似层状、团块状及不规则状主要产于蛇纹石+金云母化带内,金属矿物主要有磁铁矿、黄铁矿、黄铜矿、斑铜矿、辉铜矿、自然金等,伴有硅化、绿泥石化和碳酸盐化。成矿作用与花岗闪长岩和石英闪长岩的侵入活动密切相关,主要受北东和北西向褶皱及相关断裂控制,矽卡岩化受捷嘎组中部纹层状白云岩和砂质白云岩等有利岩性控制,矿体就位于矽卡岩带的高渗透率部位。

Geological features and ore-controlling factors of the Galale Cu-Au deposit in Tibet

Located in the northwestern part of the Gangdise polymetallic belt of Tibet, the Galale Cu-Au deposit discovered in recent years is a typical magnesian skarn-type deposit. Based on large-scale geological mapping together with previous studies, the authors systematically analyzed geological features and ore-controlling factors of the Galale Cu-Au deposit. The main strata outcropped in this area consist of dolomite and dolomitic limestone of the Lower Cretaceous Jiega Formation underlain by interbedded sandstone, siltstone and rhyolitic-dacitic volcanic rocks of the Lower Cretaceous Langjiu Formation. There are at least three phases of deformation: the first period formed NW-trending folds and NE-striking tensional cross faults, the second one formed NE-trending folds, NE-striking longitudinal compression faults and small-sized tensional cross faults in NW direction, and the third period formed nearly NS-trending normal faults. According to the temporal succession, the intrusive rocks in the mining area include porphyritic quartz diorite of late Yanshanian period, diorite-porphyrite, quartz diorite, granodiorite and granitic porphyry. The typical magnesian skarn was formed near the contact zones between quartz diorite, granodiorite and dolomite, dolomitic limestones of the Jiega Formation, and the skarn was formed in two periods: the skarn of early period is composed of olivine, humite, a small amount of spinel, garnet and diopside, whereas the wet skarn of late period is composed of serpentine, phlogopite and a small amount of epidote, superimposed upon the stem skarn or existent at the outside, forming many lithologic zones, such as olivine+spinel+humite±garnet±phlogopite zone, phlogopite+serpentine±olivine±garnet ±diopside zone, serpentine+phlogopite+epidote±diopside zone, and serpentine±phlogopite of marble zone. The orebody is mainly hosted in the serpentine+phlogopite zone, which is mostly in the form of stratiform, stratoid, massive and other irregular structures. Moreover, the main metallic minerals are magnetite, pyrite, chalcopyrite, bornite, chalcocite, natural gold and so on, accompanied by silicification, chloritization and carbonation. The mineralization in this area is closely related to the emplacement of granodiorite and quartz diorite, controlled by NE, NW-trending folds and related faults. The skarns are controlled by potential lithologic characters such as lamellar dolomite and sandy dolomite of middle Jiega Group, with the orebody located in the skarn zones of high permeability.