Massive sulfide Zn deposits in the Proterozoic did not require euxinia

Magnall, Joseph M.; Gleeson, Sarah A.; Hayward, Nicholas; Rocholl, Alexander

doi:10.7185/geochemlet.2008

Cited by 22 publications

(21 citation statements)

References 27 publications

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“…There are multiple marine transgressions that can be mapped across subbasins by the preservation of pyritic and carbonaceous facies that represent maximum flooding surfaces (MFS). Two MFS have been identified in the Teena subbasin (Magnall et al, 2020), which can be correlated across other subbasins in regional studies of the Barney Creek Formation in the southern McArthur Basin (Kunzmann et al, 2019).…”

Section: Stratigraphymentioning

confidence: 78%

“…The stratiform mineralization is located >150 m (current thickness) below the MFS in the Middle HYC unit, which contains particularly high abundances of carbonaceous material and pyrite (Fig. 3B; Magnall et al, 2020). It has been suggested elsewhere that the most reducing facies (e.g., the MFS) should be targeted in SEDEX exploration models (e.g., Emsbo, 2009).…”

Section: Controls On Mineralizationmentioning

confidence: 99%

“…The distribution of fine-grained pyrite in the Lower and Middle HYC units is highly variable. There are two generations of early-stage pyrite (py1a and py1b) that predate hydrothermal mineralization, and which therefore provide an important reference for determining the relative timing of hydrothermal activity in the Lower HYC unit (Magnall et al, 2020): (1) py1a comprises very fine grained (5-10 µm), disseminated, euhedral to subhedral crystals with minor framboids, as well as wispy aggregates that are parallel to sedimentary layering (Figs. 7, 8A); (2) py1b comprises coarser grained (>10 µm) idiomorphic crystals, either disseminated in mudstone laminations or on the margins of dolomite nodules (Fig.…”

Section: Mineralization Styles and Sulfide Paragenesismentioning

confidence: 99%

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The Teena Zn-Pb Deposit (McArthur Basin, Australia). Part I: Syndiagenetic Base Metal Sulfide Mineralization Related to Dynamic Subbasin Evolution

Hayward¹,

Magnall

Taylor³

et al. 2021

Economic Geology

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Divergent genetic models have been proposed for clastic dominant (CD-type) massive sulfide Zn-Pb mineralization in the Proterozoic Carpentaria Zn Province. Due to varying degrees of tectonic overprint, it has been difficult to accurately constrain structural and paragenetic timing aspects of the CD-type genetic model, and the most basic timing constraints (syngenetic vs. epigenetic, synextension vs. syninversion) remain debated. The recently discovered Teena Zn-Pb deposit is hosted by an exceptionally well preserved subbasin that permits relative timing relationships to be well defined. Using a combination of geophysical, structural, sedimentological, and petrographic datasets, a new model for subbasin development and syndiagenetic hydrothermal replacement mineralization is developed for the Teena mineral system. At Teena, sulfide mineralization was deposited from lateral fluid flow beneath an impermeable seal several hundred meters below the paleosurface and maximum flood surface, after formation of fine-grained diagenetic pyrite (py1) and dolomite nodules. Sulfide mineralization resulted from syndiagenetic carbonate replacement and pore space cementation where thermochemical sulfate reduction took place. The sulfide mineralization is therefore partly cospatial but not cogenetic with its thick pyritic hanging wall, and its lateral alteration footprint is much smaller than predicted by sedimentary exhalative (SEDEX) models. An additional zone of low-grade Zn-Pb mineralization in the footwall W-Fold Shale Member represents a different style of mineralization not previously reported for Carpentaria CD-type Zn deposits: it is associated with strata-bound lenses of hydrothermal dolomite (HTD) that formed by both replacement and carbonate dissolution and infill, which yielded diverse cavity-infill textures that include coarse-bladed dolomite fans cemented by interstitial sphalerite, dolomite, and quartz. Volumetrically minor Zn mineralization is also present in a fault conduit hydrothermal breccia and in hanging-wall synorogenic vein sets derived by hydrothermal leaching and remobilization of Zn from the underlying mineralized zones. Whereas both the Teena and nearby McArthur River Zn-Pb deposits are located along the northern margin of the 3rd-order Hot Spring-Emu subbasin, they formed in separate 4th-order subbasins in association with local extensional growth faults. Growth fault movement in the Teena subbasin was initiated during deposition of the W-Fold Shale Member and persisted episodically until a weak structural disconformity associated with sedimentary facies regression developed in the Upper HYC unit. Shifting patterns in depocenter location, sedimentary facies development, mineralization, and alteration zonation are attributed to progressive growth and linkage of segments of a regionally anomalous ENE-trending, synsedimentary fault zone. Similar patterns of extensional subbasin development were repeated in other Zn-mineralized subbasins throughout the River supersequence across the northern Carpentaria Zn Province, and formed in response to a short-lived episode of north-northwest–south-southeast regional extension around ca 1640 ± 5 Ma, triggered by far-field subduction events.

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Section: Stratigraphymentioning

confidence: 78%

Section: Controls On Mineralizationmentioning

confidence: 99%

Section: Mineralization Styles and Sulfide Paragenesismentioning

confidence: 99%

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The Teena Zn-Pb Deposit (McArthur Basin, Australia). Part I: Syndiagenetic Base Metal Sulfide Mineralization Related to Dynamic Subbasin Evolution

Hayward¹,

Magnall

Taylor³

et al. 2021

Economic Geology

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“…8I). Further study of the chemistry of these different pyrite generations will be necessary to assess if the chemical and isotopic composition of the diagenetic pyrite can be distinguished from the hydrothermal pyrite, as has been shown in other deposits (Large et al, 2009;Gadd et al, 2016;Magnall et al, 2020c).…”

Section: Implications For the Genesis Of And Exploration For CD Depositsmentioning

confidence: 99%

Diagenetic Controls on the Formation of the Anarraaq Clastic-Dominated Zn-Pb-Ag Deposit, Red Dog District, Alaska

et al. 2021

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The Anarraaq clastic-dominated (CD) Zn-Pb-Ag deposit (Red Dog district, Alaska, USA) has an inferred mineral resource of 19.4 Mt at 14.4% Zn, 4.2% Pb, and 73 g/t Ag and is spatially associated with a separate ~1 Gt barite body. This study presents new cross sections and petrographic evidence from the Anarraaq area. The barite body, previously shown to have formed in a shallow subsurface environment akin to a methane cold seep, contains multiple generations of barite with locally abundant calcite masses, which are discordant to sedimentary laminae, and is underlain by an interval of massive pyrite containing abundant framboids and radiolarians. Calcite and pyrite are interpreted to have formed by methane-driven diagenetic alteration of host sediment at the sulfate-methane transition (SMT). The sulfide deposit contains two zones of Zn-Pb mineralization bounded by faults of unknown displacement. The dominant hydrothermal minerals are marcasite, pyrite, sphalerite, quartz, and galena. The presence of hydrothermal pseudomorphs after barite, early pyrite resembling diagenetic pyrite associated with the barite body, and hydrothermal quartz and sphalerite filling voids formed by dissolution of carbonate all suggest that host sediment composition and origin was similar to that of the barite body prior to hydrothermal mineralization. Rhenium-osmium isochron ages of Ikalukrok mudstone (339.1 ± 8.3 Ma), diagenetic pyrite (333.0 ± 7.4 Ma), and hydrothermal pyrite (334.4 ± 5.3 Ma) at Anarraaq are all within uncertainty of one another and of an existing isochron age (~338 Ma) for the Main deposit in the Red Dog district. This indicates that the Anarraaq deposit formed soon after sedimentation and that hydrothermal activity was approximately synchronous in the district. The initial Os composition of the Anarraaq isochrons (0.375 ± 0.019–0.432 ± 0.025) is consistent with contemporaneous seawater, indicating that a mantle source was not involved in the hydrothermal system. This study highlights the underappreciated but important role of early, methane-driven diagenetic processes in the paragenesis of some CD deposits and has important implications for mineral exploration.

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“…Contrary to the SEDEX model, many researchers have made petrographic arguments that CD-type deposits formed via replacement processes during diagenesis (Grondijs and Schouten, 1937;Williams, 1978;Magnall et al, 2020a;Spinks et al, 2021). Furthermore, recent studies have shown that the protolith of CD-type deposits accumulated under a range of depositional redox conditions, albeit with minimal evidence of prolonged euxinia (Reynolds et al, 2015;Magnall et al, 2018Magnall et al, , 2020b.…”

Section: Introductionmentioning

confidence: 99%

The Teena Zn-Pb Deposit (McArthur Basin, Australia). Part II: Carbonate Replacement Sulfide Mineralization During Burial Diagenesis—Implications for Mineral Exploration

Magnall

Hayward²,

Gleeson

et al. 2021

Economic Geology

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The Teena Zn-Pb deposit is located in the Carpentaria Zn Province (Australia), which contains some of the largest clastic dominant (CD-type) massive sulfide Zn-Pb deposits in the world. The timing of the main stage of hydrothermal sulfide mineralization in the Teena subbasin is constrained to the midstage of burial diagenesis, during a period of short-lived regional extension. To distinguish hydrothermal alteration from spatially and temporally overlapping burial diagenetic alteration, and to establish the primary controls on hydrothermal mass transfer, it is necessary to evaluate the various foot- and hanging-wall alteration assemblages that formed between early- (eogenesis) and late- (mesogenesis) stage diagenesis. To achieve this, we have statistically evaluated a large lithogeochemistry dataset (n >2,500) and selected a subset (n = 65) of representative samples for detailed mineralogical (X-ray diffraction, illite crystallinity) and petrographic (scanning electron microscopy) analyses; hyperspectral core imaging data were then used to upscale key paragenetic observations. We show that sulfide mineralization was predated by multiple diagenetic alteration assemblages, including stratiform pyrite, dolomite nodules and cement, disseminated hematite and authigenic K-feldspar. These assemblages formed during eogenesis in multiple subbasins across the broader McArthur Basin and are not part of the synmineralization alteration footprint. Whereas pyrite and dolomite formed primarily from the in situ degradation of organic matter, feldspar authigenesis was the product of K metasomatism that was focused along permeable coarse-grained volcaniclastic sandstone beds within the host-rock sequence. The immature volcaniclastic input is broadly representative of the siliciclastic compositional end member in the subbasin, which formed the protolith for phyllosilicate (illite, phengite, chlorite) formation during burial diagenesis. There is no evidence of extensive phyllosilicate alteration in any of the geochemical, mineralogical (illite crystallinity), or petrographic datasets, despite some evidence of K-feldspar replacement by sphalerite in the Lower and Main mineralized lenses. Rather, the high Zn grades formed via dolomite replacement, which is resolvable from a chemical mass balance analysis and consistent with petrographic observations. There are significant exploration implications associated with carbonate-replacement sulfide mineralization during mesogenesis: (1) the capacity for secondary porosity generation in the host rock is as important as its sulfate-reducing capacity; (2) hydrothermal mineralization has a short-range cryptic lateral and vertical synmineralization alteration footprint due to acid neutralization by a carbonate-rich protolith; and (3) the distribution and chemistry of premineralization phases (e.g., pyrite, dolomite nodules) cannot be directly related to the mineralization footprint, which is localized to the 4th-order subbasin scale. Future exploration for this deposit style should therefore be focused on identifying units that contain a mixture of organic carbon and carbonate in the protolith, at favorable stratigraphic redox boundaries, and proximal to feeder growth faults.

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Massive sulfide Zn deposits in the Proterozoic did not require euxinia

Cited by 22 publications

References 27 publications

The Teena Zn-Pb Deposit (McArthur Basin, Australia). Part I: Syndiagenetic Base Metal Sulfide Mineralization Related to Dynamic Subbasin Evolution

The Teena Zn-Pb Deposit (McArthur Basin, Australia). Part I: Syndiagenetic Base Metal Sulfide Mineralization Related to Dynamic Subbasin Evolution

Diagenetic Controls on the Formation of the Anarraaq Clastic-Dominated Zn-Pb-Ag Deposit, Red Dog District, Alaska

The Teena Zn-Pb Deposit (McArthur Basin, Australia). Part II: Carbonate Replacement Sulfide Mineralization During Burial Diagenesis—Implications for Mineral Exploration

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