Sedimentary fans: A new genetic model for sedimentary exhalative ore deposits

Sedimentary-exhalative (SEDEX) deposits are one of the most important types of metal ore deposits. The genesis of such economic deposits has been problematic; thus a holistic model is urgently needed to explain their formation. Based on field surveys and geochemical analyses of the Xitieshan Pb–Zn, the Zhaokalong Fe–Cu polymetallic, and several other typical sedimentary-exhalative deposits in China, this study proposes a “sedimentary fan model” to explain such deposits. The results of this research suggest that the ore forming fluid of sedimentary-exhalative deposits can be considered as a kind of turbidity current. These fluids originated from the exhalative process itself, passing through syngenetic faults, flowing into the marine basin, and forming fan-shaped sedimentary ore deposits. The ore bodies of sedimentary fans consist of three parts: pipe, central, and marginal facies. The fans typically show zonations of mineralization, trace elements, fluid inclusions, isotopes, redox environments, etc. Pipe facies is deeply sourced and proximal to synsedimentary faults, generally constituted by unstratified, altered stockworks, exhalite (e.g., siliceous rocks) and ore bodies, and characterized by high temperatures and salinities. Central and marginal facies mainly occur as stratiform ore bodies, exhibiting typical characteristics of sedimentary origin. From the central facies to the marginal facies, increasing seawater components enter into the ore-forming process, resulting in a gradual change of metallogenic environment. This sedimentary fan model is used with satisfactory results to predict metallogenesis in the Xitieshan, the Zhaokalong and other sedimentary-exhalative deposits in China.

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