(斜长石+黑云母+石英)-NaCl(NaHCO_3)-H_2O矿物蚀变与金矿化反应研究:450～250℃和50MPa

Experimental study on the alteration of (plagioclase+biotite+quartz)-NaCl(NaHCO_3)-H_2O mineral system and gold mineralization reaction at 450～250 ℃and 50 MPa

采用(斜长石+黑云母+石英)这三种单矿物组合与1mol/LNaCl或0.5mol/LNaCl+0.5mol/LNaHCO3溶液在450～250℃和50MPa条件下反应7d。实验表明,反应后流体pH值发生了变化,NaCl介质向酸性变化,NaCl+NaHCO3介质向中性转化。溶液中K、Ca、Mg、Fe和Au含量也随之发生变化。矿物表面发生溶解和离子置换等反应。斜长石表面形成钠长石反应边,黑云母变色,石英重结晶,反应器皿金管中的金被溶解后在金管壁和黑云母表面重结晶,黑云母周边出现红色Fe2O3。在450℃的NaCl介质中,金含量可达1070μg/g,但随温度下降迅速减低,在NaCl+NaHCO3介质中,金含量较低。显然,金的活化迁移和富集与Cl、pH、Fe3+/Fe2+密切相关,金管中金起到示踪作用,显示出金在水/岩反应中的原电池效应。

Chemical reaction of plagioclase +biotite +quartz mineral mixture with 1.0 mol/L NaCl or 0.5 mol/L NaCl +0.5 mol/L NaHCO3 solution at 450～250 ℃and 50 MPa for 7 d shows that after reaction NaCl solution becomes more acidic, while NaCl +NaHCO3 solution tends to be more neutralization, and that the concentration of K, Ca, Mg, Fe and Au in the solution changes. Dissolution and ion exchange reaction on the mineral surface take place. Albite is formedon the plagioclase surface, biotite changes in color, quartz recrystallized, gold was dissolved from gold capsule and then formed a little of gold needles on the capsule surface and recrystallized on biotite surface, around which red Fe2O3emerged. In the NaCl solution of 450 ℃, Au content reaches to 1 070 μg/g, but decreases sharply with decreasing temperature. Comparatively, Au content is very low in NaCl +NaHCO3 solution. Obviously, gold activiation, transportationand enrichment are closely related to Cl, pH value and Fe3+/Fe2+ratio. Au of the capsule acts as a tracer, showing an elementary battery effect of Au in water rock reaction.