喀拉通克铜镍矿床硫同位素组成特征及其地质意义

硫同位素研究在喀拉通克岩体的地壳物质混染过程中有重要意义。通过对块状和浸染状矿石、斑点状和脉状矿石以及围岩中硫化物进行硫同位素测试,分析了黄铜矿、黄铁矿、磁黄铁矿的硫同位素在硫化物中的富集状态,探讨了喀拉通克铜镍矿床硫同位素组成特征及其地质意义。结果表明:块状矿石的同位素测定值与标准值之间的千分偏差δ(³⁴S)为(-1.30～1.84)×10^-3,浸染状矿石的δ(³⁴S)为(-2.50～0.85)×10^-3,脉状矿石的δ(³⁴S)为(-1.54～3.00)×10^-3,围岩中黄铁矿的δ(³⁴S)为(-7.8～-3.3)×10^-3;硫同位素在硫化物中的富集从大到小依次为黄铁矿、磁黄铁矿、黄铜矿,说明硫化物之间基本达到了硫同位素平衡;喀拉通克铜镍矿床的硫主要来自于地幔,只在岩浆熔离作用形成的浸染状矿石和岩浆后期热液阶段形成的脉状矿石以及晚期黄铁矿中有少量或局部地壳硫混染的痕迹;地壳硫的加入没有在岩浆源区发生,可能发生在岩浆上升并发生硫化物就地熔离的局部过程中,几乎不对硫饱和及硫化物的熔离产生影响;岩浆在地壳深部发生的橄榄石、铬铁矿等矿物的分离结晶作用,有可能是促使硫饱和与硫化物熔离的主要因素。

Characteristics of Sulfur Isotope in Kalatongke Cu-Ni Deposit and Its Geological Significance

The study on sulfur isotope is of great importance to revealing the process of crustal contamination in Kalatongke mafic-ultramafic intrusion. The concentrations of sulfur isotope of chalcopyrite, pyrite, pyruhotite in massive sulfide, disseminated sulfide, speckled and veined ores and wall rocks were analyzed; and the characteristic of sulfur isotope in Kalatongke Cu-Ni deposit and its geological significance were discussed. The results showed that per thousand deviations between measured isotope and standard values δ(³⁴S)of massive, disseminated, speckled and veined ores and pyrite in wall rock were(-1.30-1.84)×10^-3,(-2.50-0.85)×10^-3,(-1.54-3.00)×10^-3 and(-7.8--3.3)×10^-3, respectively; concentrations of sulfur isotope in sulfide were pyrite, pyruhotite and chalcopyrite in descending order, and it basically achieved sulfur isotope equilibrium among the sulfides; the sulfur in Kalatongke Cu-Ni deposit was mainly derived from mantle, traces of crustal sulfur contamination were little or partial in disseminated ores which formed in the process of magma segregation, vein ores which formed in postmagmatic hydrothermal stage, and pyrite which formed in postmagmatic later stage; the crust-derived sulfur did not enter into the magma source zone, it would be partly occurr in the process of the magma rising and sulfide segregation in situ, almost had little affect on sulfur saturation and sulfide segregation; the fractional crystallization of olivine and chromite occurred in deep crustal magma may be the major factor to promote sulfur saturation and sulfide segregation.