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Open-File Report 2009-1209

Geologic Criteria for the Assessment of Sedimentary Exhalative (Sedex) Zn-Pb-Ag Deposits

By Poul Emsbo

Abstract

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Sedex deposits account for more than 50 percent of the world's zinc and lead reserves and furnish more than 25 percent of the world’s production of these two metals. This report draws on previous syntheses as well as on topical studies of deposits in sedex basins to determine the characteristics and processes that produced sedex deposits. This analysis also uses studies of the tectonic, sedimentary, and fluid evolution of modern and ancient sedimentary basins and mass balance constraints to identify the hydrothermal processes that are required to produce sedex deposits.

This report demonstrates how a genetic model can be translated into geologic criteria that can be used in the U.S. Geological Survey National Assessments for sedex zinc-lead-silver deposits to define permissive tracts, assess the relative prospectivity of permissive tracts, and map favorability within permissive tracts.

First posted September 29, 2009

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Suggested citation:

Emsbo, Poul, 2009, Geologic criteria for the assessment of sedimentary exhalative (sedex) Zn-Pb-Ag deposits: U.S. Geological Survey Open-File Report 2009−1209, 21 p.



Contents

Introduction

Deposit Summary

Regional Geologic and Tectonic Environment

Theory of Deposit Formation

Sources of Ligands and Chemical Transport and Transfer Processes Involved in Ore Component Transport

Fluid Drive, Including Thermal, Pressure, and Geodynamic Mechanisms

Conduits or Pathways that Focus Ore-Forming Fluids

Deduced Geologic Assessment Criteria

Hierarchy of Geologic Exploration and Resource Assessment Criteria

Potential Environmental Effects of Sedex Deposits

References Cited


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