Abstract

Sparce mineralization and chemical data indicate that the unconformity at the top of the Knox Dolomite is a controlling feature in the up-dip migration of ore-bearing brines into central Kentucky. Mississippi Valley-type veins in the central Kentucky mineral district were deposited from basinal brines transmitted through the Knox Dolomite and emplaced on the Lexington dome along fault zones and fractures no earlier than Alleghenian time. Deep ground-water movement is believed to have occurred either through permeable formations within the upper portion of the Knox such as the Longview or just beneath the unconformity itself where effectively sealed by weathering products and/or by overlying impermeable beds such as the Wells Creek Dolomite. An up-dip focus was provided by the Cincinnati arch which culminates in the Lexington dome within the district. Because there is a lack of fracturing and brecciation of the vein deposits in the central Kentucky district, mineralization must postdate the latest episode of movement in the area, which is post-Pennsylvanian based on the displacements of strata of this age in the adjacent basins. Such movement could be related to the Alleghenian orogeny and perhaps is as late as the opening of the Atlantic Ocean.Analysis of cores and cuttings from two sampling intervals just below the unconformity shows the distribution of Mg and Cu to be unimodal; that of Ca, Pb, F, Ba, and Zn to be lognormal bimodal; and of Fe to be lognormal trimodal, confirming at least one epigenetic episode and suggesting that this horizon was the transport host. The geographic distribution of anomalous concentrations with respect to the Cincinnati arch suggests that Ba and metals mineralization of the district resulted from brines migrating from the Appalachian basin and F mineralization from the Illinois basin.A simple method of determining the source directions of the mineralizing fluids is proposed whereby concentrations of each element are correlated with their respective X-Y map coordinates and then converted to compass directions for a more quantitative assessment. The method yields results in good agreement with those indicated by the distribution of anomalies.

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