试论中亚造山带东部多宝山矿田斑岩铜浅成低温金系统成矿特征与矿床模型

Metallogenic characteristics and ore deposit model of porphyry copper epithermal gold system in the Duobaoshan ore field,eastern margin of the Central Asian Orogenic Belt

多宝山矿田位于中亚造山带东段,是目前我国东北地区规模最大、成矿时代最老(477~470 Ma)的斑岩铜钼浅成低温热液金成矿系统,已探明铜、钼、金储量分别可达5 Mt、0.16 Mt和130 t。从成矿系统角度,其成矿特征和矿床模型尚不清晰。本文系统分析了矿床的地质地球化学特征和成矿时代,发现该成矿系统存在两期成矿事件,以第一期为主,发生在早奥陶世;第二期为叠加成矿,发生在晚三叠世。成矿作用具有下部为隐爆角砾状铜矿化、中部为脉状铜矿化、上部为金矿化的空间结构特征,围岩蚀变从中心向两侧依次为钾化黑云母化带、青磐岩化带、黏土化带、碳酸盐化带、绢英岩化带和硅化带。成矿流体主要来源于岩浆水,从多宝山斑岩铜矿到争光浅成热液金矿床呈现大气水加入比例增大的趋势。根据第一期成矿斑岩具有高Ce^(4+)/Ce^(3+)(174~461;均值约290)、高f_(O2)埃达克质岩浆特征,进一步得出主成矿期与古生代古亚洲洋俯冲作用相关的壳幔混源岩浆作用有关。成矿受古火山机构所制约,其北西到南东成矿深度增大与剥蚀程度相关,受铜山逆断层作用效应,暗示铜山断层以南为较好的找矿靶区。最后,本文建立了该区古生代斑岩铜浅成低温热液金成矿系统的矿床模型,以期为该区进一步矿产勘探提供借鉴。

The Duobaoshan ore field,situated in the eastern part of the Central Asian Orogenic Belt(CAOB),represents the largest porphyry Cu(Mo)epithermal Au metallogenic system with an ancient mineralization age(477470 Ma)in Northeast China.The reserves of copper,molybdenum,and gold resources have been preliminarily estimated to be over 5 Mt,0.16 Mt,and 130 t,respectively.Despite this,the metallogenic characteristics and ore deposit model of this system remain unclear.This study comprehensively analyzes the geological,geochemical characteristics,and timing of the deposit.It suggests the presence of two mineralization events in the metallogenic system:the primary episode,occurring in the early Ordovician,and a subsequent superimposed mineralization event in the late Triassic.The mineralization exhibits spatial zonation,with explosive brecciated copper mineralization in the lower part,vein copper mineralization in the middle part,and gold mineralization in the upper part.Wall-rock alteration progresses from the center to both sides or from early to late,transitioning through potassic-biotite,propylitic,clay,carbonate,phyllic,and silicification alteration zones.The ore-forming fluids are identified as magmatic water,transitioning from porphyry copper to epithermal gold deposits or from Duobaoshan to Zhengguang deposits,with a trend of increasing proportions of meteoric water.The high Ce^(4+)/Ce^(3+)ratios(174461;average 290)and high f_(O2) characteristics of the adakitic magma suggest a main mineralization related to crust-mantle mixed-sourced magmatism linked to the subduction of the Paleozoic Paleo-Asian Ocean.Mineralization is controlled by ancient volcanic mechanisms,and the increase in metallogenic depth from northwest to southeast is associated with denudation levels.The presence of the Tongshan reverse fault influences mineralization,indicating the south of the Tongshan fault as a promising exploration target.Furthermore,an ore deposit model for the Paleozoic porphyry copper epithermal gold system in this region is proposed to guide future mineral exploration efforts.