The Kapalagulu intrusion in eastern Tanzania hosts a major, 420-m-thick, stratiform/stratabound platinum group element (PGE)-bearing sulfide zone—the Lubalisi reef—within a prominent, chromititiferous, harzburgite unit close to its stratigraphic base. Several features of the vertical base and precious metal distributions (in a composite stratigraphic section based upon two deep exploration drill holes) display similarities to those of offset-type PGE reefs that formed under the overall control of Rayleigh fractionation: (1) composite layering (at several scales) defined by systematic vertical variations of sulfide and precious metal contents and intermetallic ratios, indicating repeated cycles of PGE enrichment and depletion in the order Pd-Pt-Au-Cu, and (2) in the lower part of the reef, stratigraphic offsets of the precious metal peaks below peak sulfide (Cu) content. The form and geochemistry of the reef are consistent with overturns of basal liquid layers within a liquid layering system (i.e., stable density-driven stratification of a magma chamber), plus at least two minor inputs of parental magma during which the resident magma was recharged with sulfur and metals, and the effective depletion of precious metals in the magma midway through reef development. The Lubalisi reef differs from classic offset-type PGE reefs, however, principally because individual Pd, Pt, and Au enrichment peaks are coincident, not offset. The reef is set apart from other offset-type PGE reefs in three additional ways: (1) its association with olivine cumulates that crystallized soon after initial magma emplacement and well below the first appearance of cumulus pyroxene or plagioclase (implying attainment of sulfide saturation and precious metal enrichment without prolonged concentration of sulfur and chalcophile metals by normal magma cooling and differentiation), (2) the probable role of chromite crystallization in not only triggering sulfide segregation during reef formation but also facilitating precious metal enrichment in the early stages of reef development, and (3) its great width. The early stage of fractionation may also help explain the coincident precious metal peaks through its effect on apparent precious metal partition coefficients.

中文翻译：

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坦桑尼亚西部Kapalagulu侵入体的基底橄榄石堆积中的变型偏移型铂族元素礁矿化

坦桑尼亚东部的Kapalagulu侵入带拥有一个主要的，厚度为420米，层状/分层结合的铂族元素（PGE）的硫化物带-Lubalisi礁，位于靠近地层基础的显着发色的哈兹伯格岩单元中。垂直基体和贵金属分布的几个特征（在基于两个深部勘探钻孔的复合地层中）显示出与在瑞利分馏的总体控制下形成的偏移型PGE礁相似的特征：（1）复合分层（在几个尺度上）是由硫化物，贵金属含量和金属间比率的系统垂直变化所定义的，表明PGE富集和耗竭以Pd-Pt-Au-Cu顺序重复发生，并且（2）在礁石的下部，硫化物（Cu）含量以下的贵金属峰的地层偏移。礁石的形式和地球化学与液层系统中基础液层的倾覆（即岩浆室稳定的密度驱动分层）相一致，加上至少两个次要的母岩浆输入，在此期间常驻岩浆被充注。含硫和金属，并在珊瑚礁发育过程中有效地耗尽了岩浆中的贵金属。Lubalisi礁与经典的偏移型PGE礁不同，主要是因为各个Pd，Pt和Au富集峰是重合的，而不是偏移的。通过其他三种方式将珊瑚礁与其他偏移型PGE珊瑚礁区分开：（1）其与橄榄石堆积物的结合在最初的岩浆侵位后不久就结晶了，并且远低于积辉石或斜长石的首次出现（这意味着通过正常的岩浆冷却和分化不会长时间达到硫化物的饱和和贵金属富集，而不会延长硫和嗜硫金属的浓度） ），（2）亚铬酸盐结晶可能不仅在礁石形成过程中引发硫化物偏析而且在礁石发育的早期阶段促进了贵金属的富集，而且（3）其宽度很大。分馏的早期阶段也可能通过其对表观贵金属分配系数的影响来帮助解释重合的贵金属峰。