Relation Of Bitumen To Ore In The Magmont West Orebody, Viburnum Trend, Missouri

Blebs of solid bitumen from the Magmont West orebody of the Viburnum Trend were examined and analyzed in an attempt to relate hydrocarbon distribution and origin to ore genesis. The bitumen was calculated to be approximately 48 to 63 percent aliphatic and is considered to be a polymerized normal crude oil. Polymerization, which was probably caused by water-washing, hardened the bleb surfaces and appears to have "frozen" the blebs during primary migration from local source beds. Comparison of the bitumen to kerogen in local shaly partings strongly Indicates that the oil was derived locally. The polymerized oil blebs are considered to have been derived from a type II (marine) kerogen. Textural analyses indicate that oil migration occurred after lead-zinc mineralization and at temperatures that exceed normal ancient or present geothermal gradients. The following sequence of events is postulated for the Magmont West orebody: 1 Generation of hydrogen sulfide during diagenesis of a normal organic-rich carbonate sequence. 2 Introduction of pulses of hot, metal-rich fluids that resulted in: a Lead-zinc mineralization by the following reaction: Me++ + H2S ? MeS + 2H+ b Solution of carbonates by excess acid produced during the above reaction. c Brecciation of host rock in some cases. 3 Passages of the pulse resulted in: a Carbonate buffering of fluid system to more alkaline conditions. b Precipitation of dolomite c Slight temperature drop. 4 Eventually the high temperatures Introduced by heated brine caused oil generation and initiated primary migration. 5 Water-washing and mild biodegradation altered the hydrocarbon blebs to their present composition.