栗木花岗岩型钨锡矿床云英岩化特征

Characteristics of greisenization of granite-type W-Sn deposit in Limu of Guangxi

通过矿物学研究发现,云英岩化过程的主要蚀变反应有白云母的蚀变和长石的蚀变,其成矿过程:起初,原先的锡钨载体矿物在蚀变过程中发生淋滤进入成矿流体或次生矿物相,伴随着蚀变过程,成矿流体使早先沉淀的矿物相发生了重熔,使锡钨进一步的沉淀、富集,并形成一种或多种化学成分高于围岩的蚀变晕,而蚀变后期,云英岩化减弱,中低温热液蚀变发育,形成大量硫化物,伴有黝锡矿、锡石、黑钨矿和白钨矿的晶出,并与硫化物一起呈团块状产出。还有,Sn、W与F、Cl形成络合物赋存于流体,随着pH值、温度、压力条件变化的影响,络合物不稳定或络阴离子浓度的降低,使Sn、W从流体中沉淀析出。

The mineralogical study shows that the alteration activities in the process of greisenization mostly are alteration of muscovite and feldspar.At the earlier period of mineralization,the original carrier minerals of W and Sn are leached in the process of alteration and they enter into ore-forming fluid or secondary mineral facies.Through alteration the ore-forming fluid makes the early precipitated mineral facies remelted and makes tin and tungsten further precipitated and enriched.Then one or several types of alteration haloes which have higher chemical components than the wall rocks have are formed.At the later period of altera-tion,the greisenization weakens while low-to-moderate temperature hydrothermal alteration develops.Then a lot of sulfides are formed,whereas crystallization of kassiterolamprite,kassiterite,wolframite and scheel-ite occurs in crumby structure with the sulfides.Moreover,the complex formed by Sn,W,F and Cl occurs in fluids,and the complex becomes unstable and the concentration degree of complex anion drops under the effect of changes in pH value,temperature and pressure,thus Sn and W will precipitate out from the fluids.