哈萨克斯坦努尔卡斯甘大型富金斑岩铜矿地质特征及金赋存状态

摘要

努尔卡斯甘富金斑岩铜矿位于中哈萨克斯坦,是中亚成矿域西段重要的早古生代斑岩型铜金矿床,其形成与早志留世花岗闪长斑岩和石英闪长玢岩有关.矿体由浸染状、(网)脉状和角砾状矿石组成,主要产于花岗闪长斑岩、石英闪长玢岩和石英闪长岩体内以及岩体周围的火山岩地层中.矿床内发育热液磁铁矿、金红石和热液硬石膏.矿区热液蚀变强烈,早期发育青磐岩化和钾钙硅酸盐化(钾长石-阳起石化),随后广泛发育中级泥化,到晚期发育绢云母化.铜矿化与钾钙硅酸盐化和中级泥化蚀变密切相关,矿石矿物主要为黄铜矿,少量斑铜矿和蓝辉铜矿.金矿化主要与中级泥化蚀变关系密切,少量与钾钙硅酸盐化蚀变有关.金矿物主要为细粒自然金和银金矿(多小于10μm).自然金赋存在蚀变岩中,与硅酸盐矿物关系密切,分布在它们表面、颗粒之间(粒间金)、晶体内(包裹金)和内部裂隙之中(裂隙金,少量).银金矿主要呈包裹金的形式赋存在于与中级泥化蚀变相关的热液角砾岩的黄铜矿胶结物中.努尔卡斯甘斑岩铜金矿床属于高氧化-高硫岩浆-热液成矿体系,金的大规模沉淀很可能与SO2歧化反应以及磁铁矿和硬石膏大量结晶而造成的高氧化-高硫成矿热液的SO42-/H2S比值和pH显著降低有关.%Nurkazgan gold-rich porphyry copper deposit,located in Central Kazakhastan,is an important Early Paleozoic porphyry copper-gold deposit in the western Central Asian Metallogenic Domain.Copper and gold mineralization is strongly linkcd with the emplacement of Early Silurian granodiorite porphyry and quartz diorite porphyrite.Ore-bodies,composed of disseminations,stockworks and widespread hydrothermal breccias of sulfides,are occurred in granodiorite porphyry,quartz diorite porphyrite and quartz diorite,as well as the outer volcanic rocks of Zhasor Formation.Within the deposit,it is characterized by abundant of hydrothermal magnetite and anhydrite,as well as rutile.Intensively hydrothermal alteration in Nurkazgan deposits is similar to other gold-rich porphyry copper deposits in the world,including early potassic-calcic silicate alteration (K-feldspar + actinolite) and propylitic alteration,then intermediate argillic alteration which widely developed within all intrusions,and late sericitic alteration.Copper mineralization is accompanied by potassic-calcic and intermediate argillic alterations and is consist of chalcopyrite,minor bornite and digenite.However,most gold mineralization is closely associated with intermediate argillic alteration,only minor occurred in potassic-calcic silicate alteration.Based on the scanning electron microscope (SEM) observation,the occurrence of gold is mainly as fine-grained native gold and electrum.In general,the grain size of them is less than 10μm.Native gold usually occurre in alteration rocks and is closely associated with silicate minerals in spatial (such as chlorite and illite) where native gold is mainly on their surface,among their grain boundaries,as inclusions in the crystal and minor within microfractures,while electrum is mainly encapsulated by chalcopyrite that cemented the breccias with intermediate argillic alteration.Our research suggest that the magma-hydrothermal fluid system in Nurkazgan is highly oxidized and sulfur-rich,in which the decrease of SO42-/H2S ratio and pH values by crystallizition of magnetite and anhydrite and disproportionation of SO2 dissolved in the highly oxidized fluids is likely to be responsible for most of gold deposition.