Abstract The orogenic pyrite–rich Au (As, Bi, Ag) mineralization (up to 31 g/t) of the Buracao area is one of several orogenic deposits in the Brasilia Fold Belt (BFB; Central Brazil), exposed to tropical weathering that shows extensive oxidized profiles. The distribution and thickness of these gossan profiles lead to variable gold enrichments and uncertainties to gold prospecting in this region. In order to investigate physicochemical processes related to the evolution of the gossan cover and the supergene gold enrichment, we present mineralogical, textural and geochemical data from each zone of twenty gossan profiles in the Buracao area. These results show that the mineralogy and textures along the gossan profile reflect oxidation, hydrolysis, dissolution and precipitation processes controlled by different Eh–pH conditions, which are controlled by supergene conditions and hypogene ore composition. The geometry, distribution, and thickness of gossan profiles, as well as the style of gold occurrence, reflects textures of the hypogene orebodies, while the weathering has an important role in the gold chemical refining (i.e., increasing ca. 25% in gold fineness) and the distribution of gold grades along the profile. These points allowed us to identify that the leached spongy hematite–rich zone in the upper indigenous profile contains the higher fineness gold grades (i.e., the “bonanza level”), and Bi–minerals such as waylandite and bismutite that may be important pathfinders for high gold grades in these gossan profiles. Our results demonstrate that ore prospection in gossans over Au–As–Bi–Ag deposits should be done focusing on leached zones, different to that traditionally conducted in gossans related to base metal sulfide deposits that have focused on precipitation zones. The similarities between the hypogene mineralization of the Buracao area and many deposits in the BFB and worldwide encourage the application of this approach elsewhere, which improve gold prospecting in weathering profiles over orogenic deposits.

中文翻译：

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Buracão 地区（巴西利亚褶皱带，巴西）Au（As、Bi、Ag）矿床的 Gossan 矿物学、质地和金富集：对风化剖面中金矿勘探的影响

摘要 Buracao 地区富含造山带黄铁矿的 Au（As、Bi、Ag）矿化（高达 31 g/t）是巴西利亚褶皱带（BFB；巴西中部）的几个造山矿床之一，暴露于热带风化显示出广泛的氧化轮廓。这些铁板剖面的分布和厚度导致该地区金矿的富集度和不确定性。为了研究与铁壳盖层演化和表生金富集相关的物理化学过程，我们提供了布拉索地区 20 个铁壳剖面的每个区域的矿物学、结构和地球化学数据。这些结果表明，沿铁壳剖面的矿物学和质地反映了受不同 Eh-pH 条件控制的氧化、水解、溶解和沉淀过程，受表生条件和表生矿石成分控制。铁壳剖面的几何形状、分布和厚度，以及金的赋存方式，反映了下成因矿体的质地，而风化在金化学精炼中起重要作用（即金成色提高约 25%） ) 以及沿剖面的金品位分布。这些点使我们能够确定上部土著剖面中富含浸出的海绵状赤铁矿区包含更高成色的金品位（即“富矿水平”），以及可能是重要探路者的双矿物，如韦兰石和铋矿。这些铁板型材中的黄金品位高。我们的结果表明，应在金-砷-铋-银矿床的铁板上进行找矿，重点放在浸出区，不同于传统上在与集中在沉淀区的贱金属硫化物矿床相关的铁矿中进行的。Buracao 地区的次生矿化与 BFB 和世界范围内的许多矿床之间的相似性鼓励在其他地方应用这种方法，这改善了造山矿床风化剖面中的金勘探。