Selected Mineral Deposits of the Gulf Coast and Southeastern United States

Abstract

This Society of Economic Geologists field trip, held in conjunction with the 1995 annual meeting of the Geological Society of America, provides the opportunity to examine the geology and mineral resources associated with salt tectonic structures in the Gulf Coast Basin. Furthermore, •the Gulf Coast is a geologically young basin that possesses many components commonly regarded as critical for the development of sediment-hosted mineral deposits in older terranes. Metalliferous formation waters are locally present in the Gulf Coast Basin and have been proposed as modern analogs for these older ore-forming fluids. Growth faults are important features that control local depositional facies and later fluid movement. Zn-Pb-Ag sulfide concentrations occur in two principal host settings (salt dome cap rocks and shelf carbonates) in the Gulf Coast. These sulfides have the most direct genetic affinity with Mississippi Valley type ore deposits that typically occur in older sedimentary terranes, although the cap rock occurrences have similarities to SEDEX-style mineralization. Recently discovered barite mounds on the Gulf floor provide a modern analog for the seafloor discharge of metal-bearing formation waters in a sedimentary basin. The Gulf Coast host settings commonly are associated with major petroleum reservoirs. As we travel northward from New Orleans, successively older siliciclastic units will be traversed, representing fluvial-deltaic enviroments that have persisted in the central Gulf region for most of the Tertiary. The focus of the trip will be on the Winnfield salt dome in the North Louisiana Basin, particularly the WinnRock quarry which provides unequaled exposures to study detailed features related to the complex evolution of a salt dome. The diapiric environment is the focus for a complex series of interactions related to the regional and local tectonic setting, depositional systems, and basin fluid evolution and migration (commonly including petroleum). Recent investigations of the Winnfield cap rock have revealed that the cap rock records fluid events within the local sedimentary basin that may span many tens of millions of years. Older studies, including petroleum exploration along the flanks of the Winnfield dome and structural studies conducted in the former salt mine, provide additional insight into the geologic setting. This trip will examine salt dome cap rocks for evidence of their genetic mechanisms, involving complex evolutionary processes associated with dissolution of a rising halite diapir, the accumulation of less soluble components, and alteration of these materials, largely by bacterially controlled diagenetic processes that involve petroleum degradation. The cap rock contains the “fossil” components resulting from processes of petroleum degradation and fluid interactions at or just below the contemporaneous sea floor.