投稿时间：2021-11-30
修订日期：2022-07-15
网络发布日期：2022-09-09
中文摘要:北衙超大型斑岩—矽卡岩型金矿床位于金沙江-哀牢山富碱斑岩带中段，大地构造位置处于扬子板块西缘与三江特提斯构造域结合部位，其成矿与新生代富碱斑岩密切相关。前人研究均集中在富矿岩体地球化学特征，而对贫矿岩体研究甚少，控制北衙地区岩体含矿差异性的因素尚不明确。文章以北衙矿区外围白莲村、马头湾和南大坪贫矿石英正长斑岩为研究对象，运用全岩主微量、锆石U-Pb定年以及角闪石矿物学分析，讨论了北衙地区富碱斑岩岩石成因、源区特征、岩浆含水量、氧逸度等要素，并与本区富矿岩体进行对比，由此探讨其成矿的差异性。贫矿石英正长斑岩的锆石U-Pb年龄分别为（33.96±0.43）Ma、（33.26±0.30）Ma和（32.80±0.27）Ma，与金沙江-哀牢山富碱斑岩带的岩浆活动时限吻合。岩石地球化学特征显示，贫矿石英正长斑岩具有高钾富碱的特点，微量元素上显示富轻稀土元素和Ba、Rb、K、Sr等大离子亲石元素而亏损Ta、Ti和Nb等高场强元素。富碱斑岩的Rb/Sr、Nb/Ta、La/Nb以及LREE/HREE比值较高，Eu异常不明显表明北衙富碱斑岩具有壳幔混合特征。角闪石化学成分显示，贫矿岩体中的角闪石主要是绿钙闪石。通过角闪石计算其结晶时温度、压力、氧逸度和水含量等参数并与富矿岩体中的角闪石进行对比，发现北衙地区贫矿岩体角闪石结晶环境相比于富矿岩体具有高温高压的特点，且贫矿岩体相对于富矿岩体具有更低的氧逸度和更深的侵位深度。贫矿岩体更深的侵位深度意味着更大的围岩压力，难以发生对成矿有利的流体出溶；低氧逸度意味着金属元素早期就已经沉淀无法随岩浆向上运移。因此，在北衙矿区，氧逸度和侵位深度是北衙地区岩体含矿差异性的主要控制因素。
Abstract:The Beiya porphyry-skarn Au deposit is located in the middle domain of the Jinshajiang-Ailaoshan alkali-rich porphyry belt as well as at the junction of the western margin of the Yangtze Plate and the Sanjiang Tethys orogenic belt. The mineralization is closely related to Cenozoic alkali-rich porphyry. Previous studies have mostly focused on the geochemical characteristics of ore-bearing porphyry, but a little on barren porphyry. It remains obscure as to what control their contrasting ore-forming potential. In this study, we take barren porphyries in the Bailiancun, Matouwan and Nandaping as research objects, using whole rock major-trace elements, zircon U-Pb dating and amphibole mineralogy analysis, to discuss their petrogenesis, magma source, water content and oxygen fugacity, compared with ore-bearing porphyry in this area, aimed to explore the geochemical differences between ore-bearing and barren porphyries. The zircon U-Pb ages of the barren quartz syenite porphyries are (33.96±0.43)Ma、(33.26±0.30)Ma and (32.80±0.27)Ma, respectively, consistent with the magmatic time of the Jinshajiang-Ailaoshan alkali-rich porphyry belt. Geochemical characteristics show that barren quartz syenite porphyry are characterized by enrichment in alkaline and potassium, and also enriched in LREE and LILE (Ba, Rb, K, Sr), depleted HFSE (Ta, Ti and Nb). Have high Rb/Sr, Nb/Ta, La/Nb and LREE/HREE ratio and do not show obvious Eu anomalies indicate a characteristic of mixture between normal mantle and subducted oceanic crust. Chemical compositions of amphibole show that the amphibole from barren porphyry belongs to hastingsite. The crystallization temperature, pressure, oxygen fugacity and water content are calculated by amphibole composition and compared with ore-forming porphyry, it is found that amphibole from barren porphyry are characterized by high temperature and high pressure compared with ore-forming porphyry, and barren porphyry has lower oxygen fugacity and deeper emplacement relative to ore-forming porphyry. Deeper emplacement of magma indicating higher pressure of surrounding rocks make it difficult to cause fluid exsolution which is favourable for mineralization. Low oxygen fugacity resulted in the early precipitation of metal element. Thus, oxygen fugacity and emplacement deepth of magma are key factors that control their contrasting ore-forming potential.
keywords:geochemistry alkali-rich porphyry zircon U-Pb dating amphibole oxygen fugacity emplacement deepth
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基金项目:本文得到深地资源项目(编号:2016YFC0600305)、国家自然科学基金(编号:41602103)、"大兴安岭中南段有色金属基地综合地质调查"(编号:DD20190815)和"津冀重要矿产资源集中区资源综合利用与评价"项目(编号:DD20190182)联合资助
引用文本：
付小锦,李其在,刘欢,周癸武,张维涛,张长青,张盼盼,郑瑜林,李彪.2022.北衙地区贫矿和富矿斑岩对比研究——对斑岩成矿的指示意义[J].矿床地质,41(4):751~769FU XiaoJin,LI QiZai,LIU Huan,ZHOU GuiWu,ZHANG WeiTao,ZHANG ChangQing,ZHANG PanPan,ZHENG YuLin,and LI Biao.2022.A comparative study of fertile and barren porphyry in Beiya area: Indicative significance for porphyry mineralization[J].Mineral Deposits41(4):751~769
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