安徽宣城茶亭铜金矿床隐爆角砾岩特征及其成矿意义

Characteristics of Cryptoexplosive Breccia from the Chating Copper-Gold Deposits,Xuancheng,Anhui Province and Its Metallogenic Significance

安徽宣城茶亭铜金矿床是近年来在长江中下游浅覆盖区之南陵—宣城中—新生代火山—沉积盆地中新发现的一个大型矿床。文章以赋矿石英闪长玢岩侵入体内发育的隐爆角砾岩为对象,通过详细的钻孔岩心观察和显微岩相学研究,确定其地质特征并探讨其与成矿的关系。根据钻孔岩心观察确定的岩石构造特征及钻孔剖面圈定的角砾岩空间分布特征,茶亭铜金矿床发育的隐爆角砾岩呈上大下小的不规则筒状体,被隐伏的石英闪长玢岩侵入体包孕。根据角砾特征以及角砾间的裂隙和胶结物特征,可将隐爆角砾岩划分为隐爆浆屑角砾岩、隐爆热液角砾岩和隐爆破裂角砾岩三类,三类隐爆角砾岩空间上有规律地分布,以隐爆浆屑角砾岩为中心向外或向上依次过渡为隐爆热液角砾岩→隐爆破裂角砾岩→石英闪长玢岩。基于隐爆角砾岩与蚀变和矿化的关系推测,岩浆—气液隐蔽爆破作用所产生的大量裂隙为后期含矿岩浆热液和大气降水热液的运移、交代、混合乃至卸载、沉淀成矿提供了有利的构造空间。茶亭铜金矿床的矿体赋存于浅成斑岩侵入体中,其围岩蚀变类型与分带,以及矿化呈细粒浸染状和细脉—网脉状等地质特征显示其与斑岩型矿床极为相似,但矿化富集部位与隐爆角砾岩筒(体)的一致,且矿床同时发育角砾状、脉状、团块状矿化,矿脉中发育热液硬石膏甚至形成硬石膏岩等地质特征又明显不同于斑岩型矿床。因此,文章将茶亭铜金矿床确定为一个与中酸性浅成斑岩侵入体密切相关的隐爆角砾岩型矿床。

The Chating copper-gold ore in Xuancheng region is a newly discovered large ore deposit in the Mesozoic-Cenozoic volcanic-sedimentary Nanling-Xuancheng basin in recent years,where the deposits are located at shallow depths of the Middle-Lower Yangtze River.This study is focused on the cryptoexplosive breccia pipe developed in the intrusives of quartz-dioriticporphyrite in the Chating copper-gold ore deposits.Based on the detailed core observations and petrographic analysis,characteristics and types of cryptoexplosive breccia are determined,and the relationship between the cryptoexplosive breccia and the copper-gold mineralization is discussed.The cryptoexplosive breccia in the ore deposits can be divided into three types:cryptoexplosivemelt-crystal-lithicbreccia,cryptoexplosive hydrothermal breccia,and cryptoexplosive fracture breccia based on its textures,compositions and abundance of rubbles.The cryptoexplosive breccia appears as an irregular pipe enveloped by the quartz-dioriticporphyrite and shows a regular spatial distribution.From the center of breccia to wall-rock are quartz-dioriticporphyrite,cryptoexplosivemelt-crystal-lithicbreccia,the cryptoexplosive hydrothermal breccia,and the cryptoexplosive fracture breccia,respectively.The spatial relationship between the alterated,mineralized and the cryptoexplosive breccia pipe shows that there exists a genetic link between formation of cryptoexplosive breccia and mineralization.The cryptoexplosion of the melt,liquid and gas originated from intermediate-acid magma induced the formation of large amount rubbles and fractures which can cause sudden temperature and pressure changes of ore-forming fluids.In addition,the cryptoexplosive breccia may provide room for migrating,mixing,and ore-forming material unloading for ore-forming hydrothermal fluid that arose from magmatic hydrothermal fluid.The geological features of the Chating copper-gold deposit are similar to those of the porphyry deposits including the intermediate-acid porphyrite host rocks,the alteration types,and zonation of wall rocks,as well as fine-grained dissemination and fine-veined,and net-veined mineralization.However,the mineralization enrichment site is consistent with the cryptoexplosive breccia pipe.Also,the geological features such as breccia,veined,agglomerated mineralization and hydrothermal anhydrite developed intensively in the vein are distinctly different from typical porphyry deposits.Therefore,based on these characteristics,we suggest that the Chating copper-gold ore deposit is a cryptoexplosive breccia type deposit closely related to intermediate-acidic hypabyssal intrusion.