The Jacurici Complex hosts the largest chromite deposit in Brazil in an up to 8-m-thick chromitite layer within a tectonically segmented 300-m-thick intrusion. The ore has been interpreted as the result of crustal contamination-driven crystallization in a magma conduit. This study addresses the stratigraphy, mineralogical and textural relationships, and mineral chemistry of the Monte Alegre Sul segment focusing on chromite-hosted inclusions from the Main Chromitite Layer to understand the role of volatiles in the genesis of the massive chromitite. Silicate inclusions (enstatite, phlogopite, magnesiohornblende, diopside and olivine) are commonly monomineralic and sub- to euhedral, and crystallized prior to, or coeval with, the chromite crystallization. Carbonate inclusions (dolomite and magnesite) are irregular or have negative crystal shapes, suggesting entrapment as melt droplets. Sulfides (pentlandite, millerite, heazlewoodite, polydymite, pyrite, and chalcopyrite) are often polymineralic, irregular, or hexagonal-shaped, indicating entrapment as sulfide melt and as monosulfide solid solution. The inclusions indicate an H 2 O- and S-saturated resident magma with immiscible droplets of carbonate melt during chromite crystallization. Inclusion-rich and inclusion-free chromites that occur together have similar compositions and are considered to have formed from the same magma in response to variations in the degree of Cr saturation. Hot primitive magma might have heated and mobilized CO 2 and probably water from devolatized and assimilated carbonate-rich wall rocks, increasing f O 2 and triggering chromite crystallization. We propose that the formation of the chromitite layer started as in situ crystallization with additional material added by slumping of locally remobilized chromite slurries, facilitated by the presence of volatiles.

中文翻译：

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巴西 Jacurici Complex 块状铬铁矿层的岩石成因：来自铬铁矿包裹体的证据

Jacurici Complex 拥有巴西最大的铬铁矿矿床，位于一个 300 米厚的构造分段侵入体中，最高 8 米厚的铬铁矿层。该矿石被解释为岩浆管道中地壳污染驱动结晶的结果。本研究涉及 Monte Alegre Sul 段的地层学、矿物学和结构关系以及矿物化学，重点是来自主铬铁矿层的铬铁矿包裹体，以了解挥发物在块状铬铁矿成因中的作用。硅酸盐内含物（顽辉石、金云母、角闪石、透辉石和橄榄石）通常是单矿物和亚自形的，并且在铬铁矿结晶之前或与铬铁矿结晶同时期结晶。碳酸盐包裹体（白云石和菱镁矿）不规则或呈负晶形，暗示作为熔滴被捕获。硫化物（镍黄铁矿、镍铁矿、heazlewoodite、polydymite、黄铁矿和黄铜矿）通常是多矿物的、不规则的或六边形的，表明作为硫化物熔体和单硫化物固溶体被截留。包裹体表明在铬铁矿结晶过程中存在 H 2 O 和 S 饱和的常驻岩浆，具有不混溶的碳酸盐熔体液滴。一起出现的富含包裹体和不含包裹体的铬铁矿具有相似的成分，并且被认为是由相同的岩浆形成的，以响应 Cr 饱和度的变化。热的原始岩浆可能加热并移动了 CO 2 以及来自脱挥发分和同化的富含碳酸盐的围岩中的水，从而增加了 f O 2 并引发了铬铁矿结晶。