Mississippi valley-type deposits; products of brine expulsion by eustatically induced hydrocarbon generation? An example from northwestern Australia

Mechanisms for fluid flow such as compactive dewatering, gravity-driven hydrologic flow, and seismic pumping are not geologically plausible for Mississippi Valley-type (MVT) mineralization in the Lennard Shelf, Canning Basin, northwestern Australia. Sulfides at Cadjebut and the other Lennard Shelf M...

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Bibliographic Details
Published in:Geology (Boulder) 1994-04, Vol.22 (4), p.315-318
Main Authors: Eisenlohr, Burkhard N, Tompkins, Linda A, Cathles, Lawrence M, Barley, Mark E, Groves, David I
Format: Article
Language:English
Subjects:
12 Mile Bore Deposit
Australasia
Australia
Blendevale Deposit
brines
Cadjebut Deposit
Canning Basin
Economic geology
eustasy
Fitzroy Trough
genesis
Geology
geothermal gradient
heat flow
Hydrocarbons
lead-zinc deposits
Lennard Shelf
Marine
mechanism
metal ores
Minerals
mississippi valley-type deposits
Narlala Deposit
northwestern Australia
ore bodies
petroleum
temperature
unconformities
Western Australia
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Summary:Mechanisms for fluid flow such as compactive dewatering, gravity-driven hydrologic flow, and seismic pumping are not geologically plausible for Mississippi Valley-type (MVT) mineralization in the Lennard Shelf, Canning Basin, northwestern Australia. Sulfides at Cadjebut and the other Lennard Shelf MVT deposits precipitated from overpressured, hydrocarbon-rich brines. The deposits lie below a major mid-Carboniferous unconformity that is linked to a global sea-level fall. Independent evidence at Cadjebut also constrains the time of mineralization to the mid-Carboniferous. A sea-level fall at this time could have raised the sediment-water interface above the thermocline, thereby increasing the temperature of the basin by ∼16 °C. Model calculations show that a rise in basin temperature would induce sufficient hydrocarbon gas maturation to expel 1005 km3 of brine. This brine volume would be more than sufficient to transport and deposit the metal budget of the known MVT deposits on the Lennard Shelf. The existence worldwide of MVT deposits below unconformities suggests that sea level-induced hydrocarbon generation could have assisted MVT mineralization in other provinces.
ISSN:0091-7613
1943-2682
DOI:10.1130/0091-7613(1994)022<0315:MVTDPO>2.3.CO;2