Mississippi Valley-type deposits: Products of brine expulsion by eustatically induced hydrocarbon generation? An example from northwestern Australia

Eisenlohr, B.N.; Tompkins, Linda A.; Cathles, L. M.; Barley, Mark; Groves, David

doi:10.1130/0091-7613(1994)022<0315:mvtdpo>2.3.co;2

Cited by 28 publications

(7 citation statements)

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“…The hydrothermal system in some districts, however, was more complex. More recently, Eisenlohr et al (1994) proposed that the Lennard Shelf MVT deposits (northwestern Australia), which lie below a major mid-Carboniferous unconformity that is linked to a major eustatic sealevel drop, formed from overpressured hydrocarbon-rich brines. In some cases, such as the Southeast Missouri district (Clendenin et al 1994), the Nanisivik mine, Canada (Arne et al 1991), and the Blendevale deposit, Western Australia (Vernacombe et al 1995), the fluid migration appears to have been facilitated by regional-scale faults.…”

Section: Hydrothermal Systemsmentioning

confidence: 99%

Understanding Mineral Deposits

Misra¹

2000

100

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Section: Hydrothermal Systemsmentioning

confidence: 99%

Understanding Mineral Deposits

Misra¹

2000

100

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“…Fluid migration involves three possible mechanisms (Leach et al, 2010) (1) episodic overpressuring of compaction-driven fluids (Sharp, 1978;Cathles and Smith, 1983), (2) gravity-driven flow (e.g., Garven, 1985Garven, , 1995Bethke, 1986), or (3) tectonically driven "squeezing" flow (Oliver, 1986). Complementary to these three largely accepted conceptual models, shale compaction, gas-driven fluids (Eisenlohr et al, 1994), and transfer fault-driven fluids (Vearncombe et al, 1996) have all been suggested as alternative mechanisms.…”

Section: Introductionmentioning

confidence: 98%

The Touissit-Bou Beker Mississippi Valley-Type District of Northeastern Morocco: Relationships to the Messinian Salinity Crisis, Late Neogene-Quaternary Alkaline Magmatism, and Buoyancy-Driven Fluid Convection

Bouabdellah¹,

Niedermann²,

Velasco³

2015

Economic Geology

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The Touissit-Bou Beker Mississippi Valley-type (MVT) district of northeastern Morocco includes five major strata-bound Pb-Zn-Ag deposits that produced, over a century of mining, more than 70 Mt of ore at an average grade of 4.0 wt % Pb, 3.5 wt % Zn, ~1 wt % Cu, and 120 g/t Ag. Economic orebodies are hosted by a 25-m-thick sequence of unmetamorphosed, flat-lying, diagenetically and hydrothermally dolomitized carbonate platform rocks of Aalenian-Bajocian (174-168 Ma) age. The sulfide mineralization consists principally of galena and sphalerite, and occurs as open-space fillings and partial to massive replacements of medium-to coarse-grained dolostones.Throughout the district and surrounding prospects, sulfur isotope compositions of sulfide minerals range from -8.6 to 12.9‰ CDT (n = 194) and display spatial and temporal variations characterized by an overall progressive decrease of d 34 S values: (1) with advancing paragenetic sequence, and upward stratigraphic position; (2) toward distal prospects; and (3) within single grains from core to rim. Similarly, the distribution of 3 He/ 4 He ratios shows an overall lowering from 0.5 RA to <0.01 RA with advancing paragenetic stage. Conversely, lead isotope compositions of galena display fairly uniform 206 Pb/ 204 Pb (18.31-18.37), 207 Pb/ 204 Pb (15.61-15.66), and 208 Pb/ 204 Pb (38.45-38.62) ratios, which contrast significantly with the highly heterogeneous isotopic compositions ( 206 Pb/ 204 Pb = 17.76-18.49, 207 Pb/ 204 Pb = 15.61-15.70, 208 Pb/ 204 Pb = 37.76-39.55) shown by potential metal source rocks.The large variations in d 34 S values are explained in terms of inorganic and/or bacteriogenic reduction, at different rates, of seawater sulfate in seawater or pore fluids, in reservoirs both open and closed with respect to sulfate. The highly variable 3 He/ 4 He values reflect different degrees of mixing between mantle and crustal He components along the fluid flow path. Estimated contributions of the mantle-derived ( 4 He) component involved in the mineralizing fluids of the paragenetically early Zn-rich ore-stage I, and in the later Pb-rich main ore-stage II, are in the range of ~3 to 8%. With time, the mantle-derived input to the mineralizing fluids decreased, and contemporaneously the involvement of surface waters increased, consistent with the lowering of d 34 S with advancing paragenetic stage. This geochemical evolution toward lower isotopic values indicates that the Touissit-Bou Beker hydrothermal system became exclusively dominated by crustally derived fluids, and probably incorporated at shallower levels the influx of progressively larger volumes of cooler, dilute, and oxidized meteoric waters.Whole-rock and galena lead isotope compositions are consistent with a model in which metals were extracted from the local country rocks, particularly the basement Visean rhyodacites and associated siliciclastic rocks, and from the overlying Triassic to Upper Bajocian sediments. The extraction of lead likely occurred during the late Neogene, coincident with the Messin...

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“…Many MVT deposits contain hydrocarbons. Sphalerite at the Cadjebut deposit is purple because it contains so many hydrocarbon‐filled inclusions (Eisenlohr et al. 1994), for example.…”

Section: The Operation Of Gas Pulsarsmentioning

confidence: 99%

“…Many MVT deposits contain hydrocarbons. Sphalerite at the Cadjebut deposit is purple because it contains so many hydrocarbon-filled inclusions (Eisenlohr et al 1994), for example. Figure 7 shows the MVT deposits associated with the Arkoma Basin and the basal aquifer system through which Sangster et al 1994).…”

Section: The Enigmatic Nature Of Mvt Depositsmentioning

confidence: 99%

Changes in sub‐water table fluid flow at the end of the Proterozoic and its implications for gas pulsars and MVT lead–zinc deposits

Cathles¹

2007

Geofluids

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A fundamental change in the nature of sub-water table fluid flow occurred at roughly the Proterozoic-Phanerozoic boundary when organic matter began to be buried in sufficient quantities that nonaqueous fluids could occupy a significant fraction of the pore space. This allowed the formation of remarkably durable capillary seals that could trap gas in large portions (hundreds of kilometers) of a basin for hundreds of millions of years. Gas loss from these gas zones can be highly dynamic, especially during gas generation. Under the right circumstances, hundreds of cubic kilometers of gas can be rapidly discharged into adjacent permeable aquifers. In Pennsylvanian/Permian time, the Arkoma Basin may have repeatedly discharged such volumes of gas into the very permeable Cambrian sandstone and karstic carbonate aquifers of the mid-continent of the United States. This could have displaced brines rapidly enough to form the Mississippi Valley-type (MVT) lead-zinc deposits of this age that are associated with the Arkoma Basin, heating them only briefly as required by maturity indicators. Sea level rise accompanying the melting of Permian continental glaciers may have triggered the gas expulsion events. This radically new mechanism for the formation of MVT deposits is just one example of the nonlinear dynamics of gas accumulations that are possible since Late Proterozoic time.

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Mississippi Valley-type deposits: Products of brine expulsion by eustatically induced hydrocarbon generation? An example from northwestern Australia

Cited by 28 publications

References 0 publications

Understanding Mineral Deposits

Understanding Mineral Deposits

The Touissit-Bou Beker Mississippi Valley-Type District of Northeastern Morocco: Relationships to the Messinian Salinity Crisis, Late Neogene-Quaternary Alkaline Magmatism, and Buoyancy-Driven Fluid Convection

Changes in sub‐water table fluid flow at the end of the Proterozoic and its implications for gas pulsars and MVT lead–zinc deposits

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