豫西熊耳山蒿坪沟Ag-Au-Pb-Zn多金属矿床闪锌矿矿物学和微量元素组成特征及其成矿启示

Mineralogy,Trace Element Chemistry,and Their Metallogenic Implications of Sphalerites from the Haopinggou Ag-Au-Pb-Zn Polymetallic Deposit,Xiong’ershan Area,Western Henan

蒿坪沟银金铅锌多金属矿床是豫西熊耳山地区重要的铅锌多金属矿床之一,矿体主要赋存在蚀变破碎带和断裂带内,成矿与区内岩浆活动关系密切。目前该矿床的研究集中于同位素地球化学、成矿时代和成矿物质来源等方面,但从矿物角度示踪成矿过程的报道较少。本文以矿石中不同世代闪锌矿为研究对象,开展电子探针和LA-ICP-MS原位主微量元素分析,查明不同世代闪锌矿的矿物学和微量元素组成特征,以反演矿床成矿物理化学条件进而约束矿床成因类型。结果表明,该矿床中闪锌矿主要存在两个世代:第一世代闪锌矿(Sp1)呈黑褐色或浅褐色,常与黄铁矿和黄铜矿共生,相对富集Fe、Mn、Cd、Cu和In;第二世代闪锌矿(Sp2)呈黄褐色或暗褐色,与大量方铅矿共生,裂隙被它形黄铁矿和碳酸盐充填,相对富集Co、Ge、Sn和Pb。闪锌矿中主要富集的元素为Fe、Co和In,其中Fe、Mn、Cd、Co和In等元素基本是以类质同象的形式赋存在闪锌矿的矿物晶格中,而Ag、Sb、Cu和Pb可能是以子矿物或显微包裹体的形式赋存。此外,Zn/Cd、Zn/Fe和Ga/In比值以及Fe温度计指示闪锌矿形成于中低温(沉淀时流体温度为229~259℃)和低硫逸度(lgƒ(S_(2))=-12.0~-10.1)的环境下,由成矿阶段II(Sp1到成矿阶段Ⅲ(Sp2其成矿温度可能发生了显著变化,结合面扫描分析结果,指示闪锌矿从核部到边缘温度逐渐降低。通过与国内外典型铅锌矿床闪锌矿微量元素特征对比,结合本矿床闪锌矿中低的Ga/In和Ge/In比值及Ge含量的特征,指示蒿坪沟银金铅锌多金属矿床成矿过程有岩浆活动的参与。综合认为蒿坪沟银金铅锌多金属矿床可能属于岩浆期后热液蚀变岩型和脉型矿床。

The Haopinggou Ag-Au-Pb-Zn deposit is an important Pb-Zn polymetallic deposit in the Xiong’ershan area,Western Henan.The orebodies are identified as mainly occurring in the altered fractures and fault zones,and the metallogenesis of the deposit is associated with magmatic intrusions.Previous studies on this deposit mainly focuses on geochronology and isotopic geochemistry,constraining the ore-forming age and tracing ore-forming materials.Few studies focus on interpreting the mineralization processes from a mineralogy perspective.In this study,we studied the mineralogy,major and trace elements of different types of sphalerite,using EPMA and in situ LA-ICP-MS techniques,with an aim to invert the ore-forming physicochemical conditions and to constrain the genetic types of the deposit.Our study identified two types of sphalerites in this deposit.Sphalerite I contains higher Fe,Mn,Cd,Cu,and In contents,with a dark or light brown color,and is mostly associated with pyrite and chalcopyrite occurrence.Sphalerite II is relatively enriched in Co,Ge,Sn,and Pb contents,with a yellowish or dark brown color,and predominantly coexists with galena,and the fractures of sphalerite II are usually infilled by pyrite and carbonate grains.Sphalerite was investigated to have a considerable Fe,Co,and In contents,and Fe,Mn,Cd,Co,and In basically occur as substitutions in the crystal,but Ag,Sb,Cu,and Pb minerals present as mineral inclusions within the sphalerite.Moreover,the trace elements,element ratios(Zn/Cd,Zn/Fe,and Ga/In),and combined with the geothermometric result indicate a low to medium temperature(229-259℃of the ore-forming fluid)and low sulfur fugacity(lgƒ(S_(2))=-12.0--10.1)mineralized environment and the mineralization temperature may have changed significantly from stage II(Sp1)to stage III(Sp2),and the formation temperature of sphalerite grain gradually decreases from the core to the edge based on the elemental mapping analysis.Comparisons with the previous studies on sphalerite from typical Pb-Zn deposits,the low Ga/In and Ge/In ratios,as well as the low Ge content,indicated that this deposit has a close relationship with the magmatic hydrothermalism.Based on those evidence,we propose that the Haopinggou Ag-Au-Pb-Zn polymetallic deposit may belong to the post-magmatic hydrothermal alteration rock type and vein type deposit.