Evaporites; in situ sulfur source for rhythmically banded ore in the Cadjebut mississippi valley-type Zn-Pb deposit, Western Australia

“…fluid flow in a fold and thrust belt setting). A better understanding of the processes that formed these dolomites is of importance as they are often spatially associated with ore deposits (Ney, 1957; Tompkins et al. , 1994; Sangster et al.…”

Section: Introductionmentioning

confidence: 99%

Zebra dolomitization as a result of focused fluid flow in the Rocky Mountains Fold and Thrust Belt, Canada

Vandeginste¹,

Swennen²,

Gleeson

et al. 2005

Sedimentology

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Discordant zebra dolomite bodies occur locally in the Middle Cambrian Cathedral and Eldon Formations of the Main Ranges of the Canadian Rocky Mountains Fold and Thrust Belt. They are characterized by alternating dark grey (a) and white (b) bands, forming an ‘abba’ diagenetic cyclicity. These bands developed parallel to both bedding and cleavage. Dark grey (a) bands consist of fine (< 300 μm) non‐planar crystalline impure dolomite. The white (b) bands are composed of coarse (up to several millimetres) milky‐white pure saddle dolomites (b1) which are often covered by pore‐lining zoned dolomite (b2). The b phases often possess a saddle‐shaped morphology. In contrast to the replacement origin of the a dolomite, the zoned b2 dolomite rims are interpreted as a cement formed in open cavities. The b1 dolomite is interpreted as the result of recrystallization with diagenetic leaching of non‐carbonate components. All the zebra dolomites studied are (nearly) stoichiometric and are characterized by enriched Na and depleted Sr concentrations. Fe and Mn concentrations in these dolomites differ depending on the sample locality. Fluid inclusion data indicate that the dolomites formed from relatively hot (TH = 130–200 °C), saline (20–23 wt% CaCl2 eq.) fluids. A diagenetic high temperature origin is also supported by depleted δ18O values (−20 to −14‰ VPDB). A contribution of 87Sr‐enriched fluids is reflected in the 87Sr/86Sr values (0·7091–0·7123). Zebra dolomite development is explained by focused fluid flow, which exploited areas of structural weaknesses (e.g. basin‐platform, rim areas, faults, etc.). Expulsion of hot basinal brines in a tectonically active regime generated overpressures, which explains the development of secondary porosity during zebra dolomitization as well as the intra‐zebra fracturing at decimetre to micrometre scale.

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“…1) and subsurface on its western side, especially the evaporitic facies of the basal Pillara platform (Hocking et al 1995;Warren & Kempton 1997) which were the likely sulphur source for mineralization (e.g. Tompkins et al 1994;Wallace et al 2002).…”

Section: Southeastern Lennard Shelf Reef Complexesmentioning

confidence: 99%

Frasnian reef evolution and palaeogeography, SE Lennard Shelf, Canning Basin, Australia

George

Trinajstic

Chow

2009

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Frasnian reef complexes of the southeastern Lennard Shelf (northern Canning Basin) developed on tilt-block highs and their evolution was controlled by fault-related subsidence. Tectonic control on relative sea-level changes was, therefore, a major factor influencing EarlyMiddle Frasnian palaeogeography of the Lennard Shelf. However, palaeogeographic reconstruction is not consistent with simple landward (northward) backstepping and younging of reef complexes in response to basin extension and subsidence of fault blocks. Using a sequencestratigraphic approach, in conjunction with sedimentological and biostratigraphic data, we propose that two neighbouring fault blocks (Lawford area on the eastern side of Bugle Gap and the Hull platform to the north) record a similar history and that the reef complexes on those blocks were initiated at similar times. Seven phases of Early-Middle Frasnian platform growth (Fr2-8) are identified. All are bounded by third-order flooding surfaces associated with backstepping of platform margins and three surfaces (defined by conodont Zone 4, Zone 6 and late Zone 6) correlate across the two fault blocks. Only one sequence boundary has been clearly identified and a second relative sea-level fall is proposed based on a major collapse event following progradation and associated coarse siliciclastic facies. We propose that the correlation of flooding events across the SE Lennard Shelf is related to episodes of basin-margin faulting centred on the large, long (c. 25 km) faults which border these blocks (shelf-parallel faults for the Lawford block and an oblique north-trending transfer zone for the Hull block). There is limited evidence for relative sea-level falls and those recognized most likely resulted from eustatic events. The correlation between the Lawford block and Hull platform suggests linkage between major NW-trending shelf-parallel and oblique transfer faults and an evolved rift system by the Early Frasnian.

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Evaporites; in situ sulfur source for rhythmically banded ore in the Cadjebut mississippi valley-type Zn-Pb deposit, Western Australia

Cited by 38 publications

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Massive hydrothermal dolomites in the southwestern Cantabrian Zone (Spain) and their relation to the Late Variscan evolution

Massive hydrothermal dolomites in the southwestern Cantabrian Zone (Spain) and their relation to the Late Variscan evolution

Zebra dolomitization as a result of focused fluid flow in the Rocky Mountains Fold and Thrust Belt, Canada

Frasnian reef evolution and palaeogeography, SE Lennard Shelf, Canning Basin, Australia

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