北山成矿带霍勒扎德盖金矿床碲化物的发现及其地质意义

Discovery and geological significance of tellurides in the Herzhedegai gold deposit,Beishan metallogenic belt

甘肃省霍勒扎德盖大型金矿床位于北山造山带的黑鹰山弧内,含金石英脉主要赋存在早石炭世英云闪长岩内的裂隙或断裂中。流体成矿过程从早到晚划分为Ⅰ、Ⅱ、Ⅲ三个阶段,分别形成(磁铁矿)-黄铁矿-石英脉、石英-多金属硫化物脉和石英-方解石脉。本次研究通过矿相学观察、扫描电镜/能谱及电子探针分析,在该矿床Ⅱ阶段矿石样品中首次发现大量碲化物,该矿物系列主要产出在黄铁矿、石英中或其裂隙内。矿区已发现的碲化物包括碲金矿、斜方碲金矿、针碲金银矿、碲金银矿、碲银矿、碲铅矿、碲汞矿、碲铋矿等;金银矿物仅以碲化物的形成存在。Ⅰ阶段流体的硫逸度(logfS2=-11.1^-9.5)较高、碲逸度(logf Te2≤-12.8)较低,Ⅱ阶段流体显示低硫逸度(logfS2=-13.5^-10.2)、高碲逸度(logfTe2=-11.1^-7.8)特征。碲化物的发现揭示了矿床与深部幔源的紧密联系,但同时不能排除矿区英云闪长岩提供成矿物质的可能。

The Herzhedegai large-scale gold deposit is located in the Heiyingshan arc of the Beishan orogenic belt in Gansu Province. The auriferous quartz veins are mainly hosted in the faults/fractures of Early Carboniferous tonalite. The hydrothermal mineralization can be divided into three stages from early to late, namely, Ⅰ-, Ⅱ- and Ⅲ-stage, which are characterized by （magnetite）-pyrite-quartz vein, auriferous quartz-polymetallic sulfide vein and quartz-carbonate vein, respectively. Based on optical microscope, scanning electron microscope analysis with energy dispersive spectroscopy （SEM ＋ EDS） and electronprobe micro-analysis （EPMA） , it was the first time that a large number of the tellurides were discovered in the 11 -stage ore samples. These minerals mainly occur in pyrite and quartz or in their fractures, consisting of calaverite, krennerite, sylvanite, petzite, hessite, altaite, coloradoite, tellurobismuthite and so on. Up to now, the discovered Au-Ag minerals are only occurring as Au- and Ag-tellurides. In I -stage of mineralization, the fluid system has relatively high sulfur fugacity （ log/S2 = - 11.1 N--9.5 ） and low tellurium fugacity （ log/Te2 ≤ -12. 8）; in Ⅱ-stage, the fluid system has relatively low sulfur fugacity （log/S2 = -13.5 - -10. 2 ） and high tellurium fugaeity （logtTe2 = - 11.1 N -7. 8）. The discovery of the tellurides in the Herzhedegai gold deposit indicates its close relationship with the mantle, but the possible source of tonalite cannot be excluded.