甘肃北山钨矿床时空分布、矿床类型及成矿动力学背景

甘肃北山造山带经历漫长而复杂的增生造山作用并于二叠纪发生碰撞造山，引发广泛的花岗质岩浆活动及相应的钨成矿作用。前人已对这些矿床的地质地球化学特征进行大量的研究，但在成矿动力学背景、成矿时代等方面仍存在着争议。基于此，本文在前人对甘肃北山钨矿床研究的基础上，通过详细的野外调研和室内综合研究，对该区钨矿床时空分布及地质、地球化学特征进行总结，并提出成矿动力学模型。甘肃北山钨矿床集中分布于星星峡—明水古微陆块周缘及双鹰山—花牛山岛弧，可以进一步厘定为两期成矿作用，即早期早志留世—中石炭世（439～362 Ma，322～314 Ma）岛弧碰撞拼贴引发古陆壳重熔，形成携带大量钨锡成矿元素的花岗质岩浆流体，最终上升至构造有利位置成矿，是北山钨锡多金属成矿的主成矿期，矿化类型多为石英脉型黑钨矿；晚期为早二叠世—中三叠世（286～226 Ma）后碰撞伸展诱发中酸性岩浆的大规模上侵及相关的钨钼矿化，矿化类型为矽卡岩型白钨矿及斑岩型钼（钨）矿，其中钨作为钼的伴生矿种出现。

The tungsten deposits in Beishan,Gansu Province,NW China: Geochronological framework,spatial distribution and tectonic implication

The Beishan orogenic belt has undergone complex tectonic evolution, which leads to voluminous magmatism and mineralization. Numbers of tungsten deposits have been discovered in the Beishan orogenic belt though the geodynamic setting and timing of the deposits is poorly constrained. In this paper, we aim to figure out the evolution and mechanism of the mineralization, and constrain the geodynamic settings. Based on the analysis of ours and published ages, combining this study with the Late Paleozoic intrusions and associated mineralization, two episodes of magmatism and related coeval tungsten mineralization have been recognized during 286～226 Ma and 439～314 Ma. These magmatic events are well recorded throughout the Shuangyingshan-Huaniushan block and Xingxingxia-Hanshan block, representing by scattered intrusions and Precambrian sedimentary strata. The former suite shows high（⁸⁷Sr/⁸⁶Sr）i, negative ε_Nd（t）and ancient T_DM2 value, indicating an ancient crust origin, the Silurian-Carboniferous mineralization exemplified by the Hongjianbingshan, Guoqing, Yingzuihongshan and Baixianishan deposit are closely associated with subduction-accretion and generation of the Gongpoquan arc-accretionary system, whereas the latter suite shows similar（⁸⁷Sr/⁸⁶Sr）i, ε_Nd（t）and T_^DM2 characters, suggesting the Precambrian metasedimentary strata may have exerted a significant role in the magma source. The Permian-Triassic mineralization including Liushashan and Yushan deposits are attributed to continuing accretion and subsequent post collision, supporting an arc-accretion system model, which is considered to be the best explanation for the 439～314 Ma mineralization, while the 286～226 Ma mineralization were related to post-collision events.