塌山斑岩锡矿床地质特征及成矿机理

GEOLOGICAL CHARACTERISTICS AND METALLOGENIC MECHANISM OF TASHAN PORPHYRY TIN DEPOSIT

燕山晚期早阶段斑岩成岩过程自交代,即白云母化和钠长石化过程锡石晶出成矿。岩浆期后气液期亦有锡石富集,中温热液作用微弱,偶见锡石硫化物石英脉,这乃是斑岩锡矿成矿模式典型。

The cassiterite-bearing porphyry occurs as NE-extending veins or dikes. Facies changes are remarkable, with the marginal facies consisting of cassiterite-bearing quartz porphyry and the central facies of cassiterite-bearing granite porphyry. Magmatic differentiation is obvious too, and both crystallization differentiation and pneumatohydrogenetic diffenentiation are intense, resulting in intense autometasomatism.The petrometallogenic mechanism is that tin-rich granitic magma derived from lower crust and upper mantle forced its way up along the fault and fold zones under the action of strong compresso-tectonic stress. Following the crystallization of phenocrysts of quartz, plagio-clase and microperthite, the groundmass was formed as changes took place in crystallization conditions, accompanied by the precipitation of cassiterite. Especially, during crystallization-differentiation and pneumatohydrogenetic differentiation leading to intense magmatic authome-tasomatism, cassiterite would extensively crystallize along with muscovitization and albitization.