锡钨锂矿化与外围脉状铅锌银铜矿化的内在成因关系和形成机制——以内蒙古维拉斯托锡钨锂多金属矿床为例

大兴安岭南段维拉斯托锡钨锂多金属矿是近年来新发现的大型矿床,具有"上脉下体"的垂向矿化分带特征,矿集区范围内表现出以花岗岩体为中心的高温锡钨钼矿化、中温铜锌矿化、外围低温铅锌银矿化的水平分带。目前,对锡钨锂多金属矿化与外围脉状铅锌银铜矿化的内在成因关系和形成机制及深部地质背景还缺乏足够的认识。Ar-Ar年代学研究结果表明,维拉斯托锡钨锂矿区石英脉型矿石中白云母的Ar-Ar坪年龄为(131.7±1.4)Ma,显示其与外围维拉斯托铜锌矿床和拜仁达坝银铅锌矿床的成矿时代基本一致,属同一构造-岩浆活动产物。石英斑岩中铁锂云母的Ar-Ar坪年龄为(121.9±1.3)Ma,可能代表了最晚期的岩浆活动时限,暗示维拉斯托矿区存在多期次岩浆-热液活动。本次研究还获得了维拉斯托矿床东南侧磨盘山岩体边部黑云母二长花岗岩锆石U-Pb年龄为(141.6±1.5)Ma(MSWD=0.75),该年龄不仅与含矿岩体石英斑岩体的年龄一致,也与北大山高分异杂岩体的形成年龄相近,揭示了维拉斯托外围高分异花岗杂岩体深边部及其与地层接触带部位还有寻找锡多金属矿的巨大潜力。综合本次工作和大量前人工作的基础上,笔者认为大兴安岭南段稀有金属矿床都形成于大陆边缘弧后伸展和软流圈上涌的构造背景,维拉斯托锡钨锂矿化与外围脉状铅锌银铜矿化属同一岩浆-热液成矿系统,不同金属元素在不同的矿化空间内的选择性沉淀是造成元素分带性的直接原因,其成矿特征上可类比南美玻利维亚锡银成矿带。值得提出的是,维拉斯托矿区岩石组合与松潘-甘孜造山带与锂矿化有关的片麻岩穹窿群类似,锡林郭勒杂岩可能为成矿提供了部分物质来源,对于岩浆-变形-变质-深熔作用过程及对稀有金属成矿的制约还需要进一步研究。

Formation mechanism and intrinsic genetic relationship between tin-tungstenlithium mineralization and peripheral lead-zinc-silver-copper mineralization: Exemplified by Weilasituo tin-tungsten-lithium polymetallic deposit, Inner Mongolia

he Weilasituo Sn-polymetallic deposit is a large deposit recently discovered in southern Da Hinggan Mountains. This deposit shows a typical "upper veins+underneath mineralized granite" mineralization zoning. Besides, the ore concentration area shows horizontal mineralization zoning:from the inner granite body outward, there exist high-T Sn-W-Mo mineralization, middle-T Cu-Zn mineralization and peripheral low-T Pb-Zn-Ag mineralization. The intrinsic genetic relationship between tin-tungsten-lithium polymetallic mineralization and peripheral veintype lead-zinc-silver-copper mineralization, the formation mechanism and the deep geological background remain insufficiently understood. The Ar-Ar chronological study shows that the Ar-Ar plateau age of muscovite in the quartz vein-type ore in the Weilasituo tin-tungsten-lithium mining area is(131.7±1.4)Ma, which is consistent with the ore-forming ages of the peripheral copper-zinc mineralization and silver-lead-zinc mineralization and hence they belong to the same products of the tectonic-magmatic activities. The Ar-Ar plateau age of the zinnwaldite in quartz porphyry is(121.9±1.3) Ma, which may represent the latest time limit of magmatic activity, suggesting that there were multiple magmatic-hydrothermal activities in the mining area. The zircon U-Pb age of biotite monzogranite in the southeastern part of the Weilasituo deposit is(141.6±1.5)Ma (MSWD=0.75), which is not only consistent with the age of the ore-bearing rock of quartz porphyry, but also consistent with the age of the formation of the Beidashan high-differentiation complex, revealing the great tin-polymetallic prospecting potential in the peripheral area and/or in the deep part of the peripheral high-differentiation granite complex in the Weilasituo deposit. On the basis of this study and large numbers of previous research results, the authors believe that the rare metal deposits in the southern part of the Da Hinggan Mountains were formed under the tectonic background of lithospheric extensional and thinning environment. The Weilasituo tin-tungsten-lithium mineralization and peripheral vein-type lead-zinc-silver-copper mineralization belong to the same magma-hydrothermal metallogenic system, and the selective precipitation of different metal elements that occurred in different spaces is the direct reason for the elementary zonation. Moreover, its metallogenic characteristics can be analogous to those of the Bolivian tin-silver ore belt in South America. It should be pointed out that the mineral assemblages in the Weilasituo deposit are similar to those of gneiss domes associated with lithium mineralization in the Songpan-Garze orogenic belt. The Xilinguole Complex may have provided some ore-forming sources. The process of magma-deformation-metamorphism-anatexis and the constraints on rare metal mineralization deserve further study.