浙江安吉铅锌多金属矿床岩浆侵位序列与成矿控制

Magmatic intrusive series and their implication for the ore prospecting in Anji exploration area,Zhejiang Province

本文在野外地质调研基础上,通过室内岩矿相鉴定和岩石化学分析,结合锆石U-Pb年代学研究结果,对安吉矿区主要侵入岩单元的岩浆侵位序列、岩浆演化、构造背景及矿化控制进行了探讨。矿区岩浆活动时限为141～117Ma,处于晚侏罗-早白垩世中国东部构造活化和构造机制转化阶段。矿区不同侵入岩单元的侵位顺序依次为黑云母二长花岗岩、正长花岗岩、花岗闪长岩、细粒花岗岩及双峰式脉岩组合,除双峰式脉岩组合外,其余岩石单元构成坞山关杂岩体。杂岩体不同岩石单元间具有一定的地球化学亲缘关系,其成分变化是先存断裂的多次张开和焊结、深源物质注入和结晶分异联合作用的结果。双峰式脉岩组合是区域岩石圈减薄高峰、深部物质快速上涌的表现,也是中国东部应力场进入引张阶段的标志。矿区主要经历了两次矿化事件。第一期与花岗闪长岩(137Ma)侵位有关,形成以石榴子石矽卡岩为特征的矽卡岩型铁铜矿化,其主要分布于矿区西部;第二期为与细粒花岗岩(134～135Ma)侵位有关的铅锌(银)、钼矿化,形成了以绿帘石矽卡岩为主的矽卡岩型铅锌(银)矿化,同时在矿区北部的石灰岩地层中形成了碳酸盐交代型铅锌矿化、在黑云母二长花岗岩中形成脉状、网脉状铅锌矿化及网脉状-浸染状辉钼矿化。主要侵入岩单元的岩石化学表明,与成矿有关的花岗闪长岩显示了I型花岗岩的地球化学特征,而细粒花岗岩的岩石化学特征界于I型与S型之间,但均表现有深源物质加入,细粒花岗岩相对于花岗闪长岩显示相对氧化条件和较强的分异特征。深源物质加入和进一步的结晶分异是造成熔体中成矿金属元素富集的重要机制。矿区内与成矿有关的花岗闪长岩和细粒花岗岩主要发育于矿区东西两侧,因此矿区西侧为铁铜勘查的有利地区,而东部的铅锌(银)钼矿化值得进一步工作,但矿区后期NE和近EW向断裂构造对矿体的保存条件影响较大,因此在勘查工作中应加强矿区构造地质方面的研究工作。

Based on field observation, petrographic and lithogeochemical results, together with zircon U-Pb chronology results, this paper discusses the intrusive sequence in Anji deposit and their evolution link, tectonic setting, as well as the mineralization implication of varied intrusive units. The magmatic intrusions in this area occur during Late Jurassic-Early Cretaceous （141 ～ 117Ma）, and they are the products of tectonic reactivation and tectonic conversion in eastern China during Late Mesozoic. The intrusive sequences are from early biotite monzonitic granite followed by syenogranite, granodiorite, finecrystalline granite and bimodal dikes. Except biomodal dikes, the other four units compose the Wushanguan complex. Geochemical affinity and compositions difference of the units in the complex may result from mantle material injection and crystallization differentiation of magma during faults activation at Late Jurassic-Early Cretaceous. The bimodal dikes marked lithospheric thinning peak and mantle material upwelling, as well as the stress field conversion into extension in eastern China. Two metallogenic events are recognized in Anji area including early Fe-Cu metallogenic event which genetically related to granodiorite and late Pb-Zn （Ag） -Mo metallogenic event which is associated with fine-crystalline granite. Geochemically, the granodiorite shows I-type granite character, whereas the fine-grained granite shows the combined character of S-type and I -type granite, and both show more mantle materials input than the other units in Wushanguan complex. Mantle materials involving and strong differentiation may be the reason for metal dements （ e. g. Fe, Cu, Mo, Pb, Zn and Ag） enrichment and related mineralization. The causative intrusive units occurs in the west and east part of the deposit respectively, so, the west of the deposit is the favorable Fe-Cu exploration area, and the east of the deposit is the favorable Pb-Zn （Ag） as well as Mo exploration area. Well-developed post-mineralization NE and EW faults have seriously influence to the preservation of ores, so the structure geology studies are very important to further exploration in Anji area.