Petrogenesis of Komatiites, Kambalda, Western Australia

西澳大利亚州坎巴尔达的硫化镍矿床是与太古宙科马提岩伴生的硫化镍矿床的典型例子。坎巴尔达的地层学和火山学关系表明，最底层的水流是沟道化的，它们可能吸收了下面的沉积物和玄武岩，这可能导致了硫化物分离，改变了岩浆与硫化物的比例，并影响了硫化物矿石的组成。评估这一过程的一个基本要素是确定寄主单位经历的杂交程度。虽然有大量的地球化学和同位素证据表明，伴生的科马提质玄武岩在上升过程中受到了花岗岩壳的污染，但由于熔岩流动的动力学性质和关键地区缺乏详细的地球化学数据，阻碍了对科马提岩中杂化作用的地球化学识别。该项目的目的是利用从钻石钻芯和地下矿工洞口特别挑选的样品的微量元素地球化学，评估基本宿主单元内和科马提岩序列之间的杂交程度。地球化学分析将采用波长色散X射线荧光光谱分析和同位素稀释质谱分析。低级别区域变质作用期间的交代蚀变将利用物质平衡计算进行评价，并将重点放在活动性最小的微量元素上。杂化程度将通过线性最小二乘混合计算来确定，分离结晶和同化的综合效应将被热力学模拟。这一研究成果将在太古宙地质、火山学、经济地质等领域具有广泛的应用前景。

The nickel sulfide deposits at Kambalda, Western Australia are the type-examples of Archean komatiite-associated nickel sul- fide ores. Stratigraphic and volcanological relationships at Kambalda suggest that the lowermost flows were channelized, that they may have assimilated underlying sediments and basalts, and that this may have induced sulfide separation, modified magma: sulfide ratios, and influenced the composition of the sulfide ores. An essential element in the evaluation of this process is a determination of the degree of hybridization experienced by the host units. Although there is abundant geochemical and isotopic evidence that associated komatiitic basalts have been contaminated by granitic crust during ascent, geochemical recognition of hybridization in the komatiites is hampered by the dynamic nature of the lava flows and a paucity of detailed geo- chemical data in critical areas. The purpose of this project is to evaluate the degree of hybridization within the basal host units and across the komatiite sequence, using the trace element geochemistry of specially selected samples taken from diamond drill core and underground miner openings. Geochemical analyses will be performed by wavelength dispersive X-ray fluorescence spectrometry and isotope dilution mass spectrometry. Metasomatic alteration during low grade regional metamorphism will be evaluated using mass balance calculations and emphasis will be placed on least-mobile trace elements. The degree of hybridi- zation will be established by linear least-squares mixing calcu- lations and the combined effects of fractional crystallization and assimilation will be modeled thermodynamically. The results of this study will have wide applications in the fields of Archean geology, volcanology, and economic geology.