T. K. Kyser

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Sandstone Diagenesis in the Mount Isa Basin: An Isotopic and Fluid Inclusion Perspective in Relationship to District-Wide Zn, Pb, and Cu Mineralization

Economic Geology (2006)

P. A. Polito T. K. Kyser P. N. Southgate M. J. Jackson

The western succession of the Mount Isa basin in northwest Queensland hosts four supergiant Zn-Pb ± Cu deposits and numerous smaller Cu and Zn-Pb deposits. Mineralization is primarily hosted in carbonaceous and calcareous shales and siltstones belonging to the 1670 to 1575 Ma Isa superbasin, but little is known about the source of metals that formed these deposits. The underlying clastic and volcanic successions belonging to the 1800 to 1750 Ma Leichhardt superbasin and the 1735 to 1690 Ma Calvert superbasin are potential metal source rocks and host a variety of diagenetic minerals that preserve geochemical information about the evolution of brines in the basin. Quartz overgrowths and pressure solution features formed during shallow burial in all clastic lithologic units but are particularly common in the well-sorted, marine-dominated units that became aquitards due to the porosity-occluding diagenetic cement. Microthermometry on fluid inclusions in the quartz overgrowths indicates formation between 100° and 174°C from a low-salinity, 2.7 to 9.1 wt percent NaCl equiv fluid (fluid 1). These data together with sequence stratigraphic mapping, basin reconstruction, and stable isotope values from the quartz overgrowths show that the diagenetic aquitards formed at 18 O fluid and δ D fluid values of 4.5 ± 4.2 and −34 ± 14 per mil, respectively, indicating evolution from a seawater-dominated source. Silicate dissolution and the widespread formation of diagenetic illite and chlorite occurred late, during deep burial diagenesis and primarily in the proximal fluvial lithologic units. These units are recognized as diagenetic aquifers and they occur adjacent to and within the Eastern Creek and Fiery Creek Volcanics where metals could have been sourced. Basin reconstruction shows that the diagenetic aquifers formed at depths between 5 and 10 km. Illite and chlorite extracted from the diagenetic aquifers have distinct δ 18 O fluid and δ D fluid values of 4.5 ± 2.8 and −63 ± 11 per mil, respectively, indicating evolution from a meteoric fluid with a variable marine contribution. These isotopic values cannot be differentiated from published isotopic values of fluid inclusion water in quartz-dolomite-chalcopyrite veins at Mount Isa or sphalerite and illite from the Century Zn deposit and the Zn lodes from the Burketown mineral field. This suggests that the diagenetic aquifers were likely source rocks for metals in the deposits in the Mount Isa basin. In contrast to the phyllosilicates in the diagenetic aquifers, regional dolomitic grainstones and dolomudstones in the Lawn Hill platform precipitated from fluids with δ 18 O fluid between −2.6 and 1.1 per mil and δ 13 C fluid between −8.6 and −3.9 per mil. This suggests that these units did not contribute to the ore-forming brines. Quartz veins formed during the later diagenetic history in the Mount Isa basin from a low-salinity brine, between 2.7 and 10.4 wt percent NaCl equiv (fluid 2). Oxygen isotope geothermometry on quartz-hematite pairs indicates that these veins formed at approximately 230°C. Crosscutting relationships reveal that a subsequent generation of quartz veins host fluid inclusions with a distinctly saline brine, with compositions between 11.9 and 23.2 wt percent NaCl equiv (fluid 3), indistinguishable from fluid inclusion compositions recorded in sphalerite from the Century and Walford Creek Zn deposits in the Lawn Hill platform and the quartz-dolomite-chalcopyrite veins at Mount Isa. Some of these quartz veins formed at ca. 400°C, based on quartz-hematite geothermometry, but fluid inclusion homogenization temperatures between 86° and 260°C suggest that another set of quartz veins, also containing high-salinity fluid inclusions, is preserved in the basin but formed at lower temperatures. Irrespective of formation temperature or timing, it is noteworthy that quartz veins hosting high-salinity fluid inclusions have δ 18 O fluid and δ D fluid values that are indistinguishable from those recorded by (1) illite and chlorite in the diagenetic aquifers, (2) fluid inclusion water in sphalerite and synore quartz and illite in the Zn deposits in the Lawn Hill platform, and (3) various alteration minerals from the Mount Isa Cu deposit. Collectively, this suggests that the quartz veins represent fluids that migrated along faults from the diagenetic aquifers during late diagenesis to form the low-temperature Zn-Pb deposits between 1650 and 1575 Ma and later during the Isan orogeny to form the high-temperature Cu deposits. Metamorphic quartz-hematite ± feldspar ± chlorite veins exist in the basin and formed between 325° and 450°C during the Isan orogeny from a brine having salinities between 12.6 and 23.2 wt percent NaCl equiv (fluid 4). These veins have distinct δ 18 O fluid and δ D fluid values of 11.8 ± 2.0 and 30 ± 2 per mil, respectively, consistent with formation from fluids derived from graywackes and arkoses during greenschist facies metamorphism. The last recognized fluid identified in the basin (fluid 5) is only found in secondary fluid inclusions that form trails across earlier formed quartz veins. This fluid was trapped after the Isan orogeny, has a low salinity, between 0.0 and 8.1 wt percent NaCl equiv, records temperatures between 131° and 256°C, and is indistinguishable from postore fluids that have been reported in the Mount Isa Cu deposit and the Zn lodes in the Burketown mineral field.

10.2113/gsecongeo.101.6.1159

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Citations (30)

Multicycle Holocene dolomite in cool-water carbonate sediments Lacepede Shelf, South Australia

AAPG Bulletin (1991)

Yvonne Bone Noël P. James T. K. Kyser

Modern carbonate sediments on the Lacepede Shelf contain up to 10% dolomite particles, as either single rhombs or clusters. The rhombs vary from sharply edged crystals and nonabraded to slightly worn to completely rounded rhombs. These groups probably represent different times of formation and transportation during Holocene glacioeustatic sea-level changes. The abraded aggregates that are loosely cemented by calcite occasionally have pristine rhombs attached. Color varies from transparent and colorless or light orange to dark red, without apparent pattern. Cathodoluminescence shows distinctive zoning, analogous to nearby mid-Cenozoic dolomites. Similarly the dolomite is Ca-rich (43 mole % Mg). It occurs within bryozoan-bivalve sediments that are a mixture of relict and modern bioclastic components, across the entire shelf, from siliciclastic sediments debouching from the Murray River to completely carbonate sediments at the shelf edge. Greatest concentrations are fund adjacent to seafloor highs, sites of abundant bryozoan, sponge, and coralline algae growth. Stable isotope values, however, are compatible with precipitation from seawater, similar to those of associated living brachiopods and Mg-rich bryozoans. Sr isotopes confirm the time of formation as modern, unlike the mid-Cenozoic time of formation for similar Tertiary dolomites. These multicycle rhombs and rhomb clusters may therefore be the nucleii formore » epitaxial precipitation of dolomite either on the modern sea floor or later during burial.« less

Siliciclastic

Carbonate minerals

Source

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Citations (1)

Uranium, thorium isotopic analyses and uranium-series ages of calcite and opal, and stable isotopic compositions of calcite from drill cores UE25a 1, USW G-2 and USW G-3/GU-3, Yucca Mountain, Nevada

Antarctica A Keystone in a Changing World (1985)

B. J. Szabo T. K. Kyser

Fracture and cavity filling calcite and opal in the unsaturated zone of three drill cores at Yucca Mountain were analyzed for uranium and stable isotope contents, and were dated by the uranium-series method.Stable isotope data indicate that the water from which the calcite precipitated was meteoric in origin.The decrease in 18 0 and increase in 13 C with depth are interpreted as being due to the increase in temperature in drill holes corresponding to an estimated maximum geothermal gradient of 43° per km.Of the eighteen calcite an opal deposits dated, four of the calcite and all four of the opal deposits yield dates older than 400,000 years and ten of the remaining calcite deposits yield dates between 26,000 and 310,000 years.The stable isotope and uranium data together with the finite uranium-series dates of precipitation suggest complex history of fluid movements, rock and water interactions, and episodes of fracture filling during the last 310,000 years.

10.3133/ofr85224

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Citations (6)

U AND Pb ISOTOPE ANALYSIS OF URANIUM MINERALS BY ION MICROPROBE AND THE GEOCHRONOLOGY OF THE McARTHUR RIVER AND SUE ZONE URANIUM DEPOSITS, SASKATCHEWAN, CANADA

The Canadian Mineralogist (2002)

Mostafa Fayek T. K. Kyser Lee R. Riciputi

A method for in situ U–Pb isotopic analyses by secondary ion mass spectrometry (SIMS) has been developed for uranium minerals with a range of chemical compositions. This method combines the advantages of conventional U–Pb dating (i.e., use of concordia) and in situ analysis, and therefore is ideally suited for the study of chemically complex and fine-grained uranium oxides associated with uranium deposits. An ion-yield normalizing coefficient (� SIMS) that accounts for variation in relative ion-yields with chemical composition of the mineral of interest was calculated using uraninite standards that cover a range of U

Geochronology

Microprobe

Uranium ore

10.2113/gscanmin.40.6.1553

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Citations (82)

ORIGIN OF URANOUS AND URANYL MINERALS AT THE CENTENNIAL DEPOSIT, ATHABASCA BASIN, NORTHERN SASKATCHEWAN, CANADA

The Canadian Mineralogist (2012)

Paul Alexandre Yulia Uvarova T. K. Kyser

Both uranous and uranyl minerals are present in the Centennial unconformity-type U deposit situated in the SW Athabasca Basin, Canada. At least two generations of uraninite are present (disseminated and massive), often strongly altered to coffinite, followed by minor fibrous coffinite forming in veins. Uranyl minerals, mostly uranophane with minor haiweeite precipitating in veins and in hand sample-scaled breccias, are present in significant amounts ( ca . 5% of the ore) not observed elsewhere in the Athabasca Basin. The multi-stage evolution of the Centennial deposit is explained by the existence of high permeability conduits, promoting the recurrent circulation of P-rich fluids that remobilized U locally. Stable isotopes composition of uranophane (δD of ca . –130 ‰ and δ 18 O of ca . 6 ‰) suggests that recent oxidizing meteoric fluids penetrated to the unconformity (at a depth of ca . 800 m) via the major Dufferin lake fault.

Centennial

Uranyl

10.3749/canmin.50.3.693

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Citations (3)

Ediacaran stromatolites and intertidal phosphorite of the Salitre Formation, Brazil: Phosphogenesis during the Neoproterozoic Oxygenation Event

Sedimentary Geology (2017)

R.A. Caird Peir K. Pufahl Eric E. Hiatt Maísa Bastos Abram Antonio José Dourado Rocha

Stromatolite

Phosphorite

Snowball Earth

Microbial mat

10.1016/j.sedgeo.2017.01.005

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Citations (48)

Brachiopods in Epeiric Seas as Monitors of Secular Changes in Ocean Chemistry: A Miocene Example from the Murray Basin, South Australia

Journal of Sedimentary Research (2006)

Peir K. Pufahl N. P. James T. K. Kyser Jeff J. Lukasik Y. Bone

Abstract Early and middle Miocene cool-water carbonates from the Murray Basin, South Australia, preserve an excellent stable-isotope record of ocean-climate change. These variably fossiliferous heterozoan deposits accumulated on a low-energy, mesotrophic, centripetal epeiric ramp during a gradual shift in climate from cool, wet conditions and abundant continent-derived nutrients to a seasonal, arid climate with reduced delivery of trophic resources to the marine realm. Temporal trends in δ13C and δ18O from unaltered brachiopods record an epeiric sea response to this warming. The globally recognized middle Miocene Monterey Event (~ 17 to 13.5 Ma) dominates the carbon isotope record, albeit with higher (~ 0.5‰) than open-ocean δ13C values. Such higher δ13C values are attributed to an increase in benthic carbonate production that accompanied climate change and the relatively short seawater mixing times characteristic of epeiric-sea systems. The Murray Basin oxygen isotope curve contains lower δ18O values (~ 2.0‰ lower) than those of the deep-sea record. This difference is ascribed to the warmer seawater temperatures (~ 17 to 22°C) that prevailed across the Miocene Murray Basin. These results show that the isotope chemistry of epeiric-sea brachiopods can be a reliable gauge of regional and global environmental evolution. Although diagenetic overprinting from meteoric cement-filled punctae and local forcing factors introduce noise that mutes isotopic signals, the open-ocean secular record is clearly discernible.

Secular Variation

10.2110/jsr.2006.079

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Citations (12)

Economic Geology (2006)

Márcia Abrahão Moura Nilson Francisquini Botelho Gema R. Olivo T. K. Kyser

The Serrinha gold deposit in the Juruena-Teles Pires gold province is spatially and genetically related to the hydrothermal alteration of the I-type calc-alkaline 1872 ± 12 Ma Matupa monzogranite in the south-central Amazonian craton. The mineralized areas are characterized by intense hydrothermal alteration of the monzogranite, comprising incipient autometasomatism, K silicate, sodic, Mn chlorite, phyllic, carbonate, and microcline alteration, with partial overprinting of the early alteration by later stages. A distal barren propylitic zone is interpreted from drill core. The gold mineralization is disseminated in the most altered samples and genetically related to Mn chlorite, K silicate, and phyllic hydrothermal alteration types. Hydrothermal magnetite and rutile are ubiquitous within pyrite. The early Serrinha gold mineralization stage is characterized by Ag-poor gold included in pyrite (Au/Ag ~7‐15), associated with pyrrhotite, cubanite, and galena. The fluids interpreted to be associated with this early auriferous stage were found only in quartz from the Mn chlorite alteration and are typically saline (45‐57 wt % NaCl equiv) and high-temperature (375° and 480°C) H2O-NaCl-KCl fluids entrapped at pressures of at least 1.3 kbars. The late-stage gold mineralization, which is coeval with the phyllic alteration, occurs either as isolated gold grains or as fracture-fillings and/or inclusions within pyrite associated with tetradymite, galena, tsumoite (BiTe), hessite (Ag2Te), and aikinite (PbCuBiS3). Gold grains associated with this late stage are richer in Ag (Au/Ag ~2‐5). Data from chlorite geothermometry and aqueous-carbonic and saline (NaCl-KCl) fluid inclusions associated with this second auriferous event indicate P-T conditions of 1.5 to 2.4 kbars and 293° to 365°C. The occurrence of lower temperature coeval aqueous, aqueous-carbonic, and carbonic fluid inclusions with no postentrapment modification in the K silicate assemblage, partially overprinted by phyllic alteration and in phyllic assemblages, suggests that fluid immiscibility and/or mixing with meteoric water occurred in the hydrothermal system. H2O-NaCl-CaCl2 fluids contemporaneous with carbonate and late microcline alteration, which postdated gold mineralization, were entrapped at lower temperatures (172°‐200°C). Calculated δ18O and δD values are 8.2 and ‐37 per mil, respectively, for the early saline fluids in equilibrium with the Mn chlorite assemblage and 1.7 to 4.7 and ‐20 to ‐15 per mil for the late fluids in equilibrium with the phyllic assemblage. These data in conjunction with fluid inclusion results suggest that early fluids exsolved from granitic melts and later mixed with meteoric water. Gold is interpreted to have been initially transported from the crystallizing magma as chlorine complexes in a hot, saline, acidic, and oxidized fluid. Decrease in temperature during fluid ascent, immiscibility, or pH increase is interpreted to have caused gold precipitation. Subsequent dilution of the saline fluid could have been responsible for the deposition of late gold in pyrite fractures. Based on field, petrological, mineralogical, fluid inclusion, and isotopic evidence, we propose that Serrinha is a typical proximal intrusion-related gold deposit, similar to porphyry-style gold deposits.

Uraninite

10.2113/gsecongeo.101.3.585

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Citations (38)

The Marcona Magnetite Deposit, Ica, South-Central Peru: A Product of Hydrous, Iron Oxide-Rich Melts?

Economic Geology (2010)

Hongmei Chen Abram H. Clark T. K. Kyser

Marcona, the preeminent Andean magnetite deposit (1.9 Gt @ 55.4% Fe and 0.12% Cu), is located in the iron oxide copper-gold (IOCG) subprovince of littoral south-central Peru. Fe oxide and Cu (-Zn-Pb) sulfide mineralization was controlled by northeast-striking faults transecting a Middle Jurassic (Aalenian-to-Oxfordian) andesitic, shallow-marine arc and a succession of contiguous, plate boundary-parallel, Late Jurassic to mid-Cretaceous volcanosedimentary basins. At Marcona, hydrothermal activity was initiated in the earliest Middle Jurassic (161–177 Ma) by high-temperature Mg-Fe metasomatism represented by cummingtonite and phlogopite-magnetite assemblages. Subsequently, during the terminal eruptions (156–162 Ma) of the arc, widespread albite-marialite alteration (Na-Cl metasomatism) was followed by the emplacement of an en echelon swarm of massive magnetite ore-bodies with subordinate, overprinted magnetite-sulfide assemblages, hosted largely by Paleozoic metasilici-clastics. The magnetite orebodies exhibit abrupt, smoothly curving contacts, dike-like to tubular apophyses, and intricate, amoeboid interfingering with dacite porphyry intrusions. There is no convincing megascopic or microscopic evidence for large-scale Fe metasomatism associated with the main, sulfide-poor mineralization. The largest, 400 Mt Minas 2-3-4 orebody is interpreted as a bimodal magnetite-dacite intrusion comprising commingled immiscible melts generated through the dissolution of metasedimentary quartz in parental andesitic magma. Oxygen and sulfur stable-isotope geothermometry indicates that the evolution at ca. 159 Ma from magnetite-biotite-calcic amphibole ± phlogopite ± fluorapatite to magnetite-phlogopite-calcic amphi-bole-pyrrhotite-pyrite assemblages coincided with quenching from above 800° C to below 450°C and the concomitant exsolution of dilute aqueous brines. Subsequently, chalcopyrite-pyrite-calcite ± pyrrhotite ± sphalerite ± galena assemblages, in part metasomatic, were deposited from lower temperature (≤360°C) brines. The Cu-poor Marcona (“Kiruna-type”) magnetite and Cu-rich IOCG deposits in the district, therefore, although spatially contiguous, represent contrasting ore deposit types. The former are interpreted as the product of Fe oxide melt coexisting with dacite magma within an andesitic arc which failed during the closure of a back-arc basin. The weak associated magmatic-hydrothermal Cu sulfide mineralization at Marcona was generated through melt vesiculation and contrasts with the considerably higher grade Cu- and Ag-rich orebodies of the major Cu-rich IOCG deposits in the Central Andes, e.g., La Candelaria-Punta del Cobre, Mantoverde, Raul-Condestable, and Mina Justa, which were the products of cool, oxidized, hydrothermal fluids plausibly expelled from the adjacent basins during tectonic inversion.

Metasomatism

Stockwork

10.2113/econgeo.105.8.1441

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Citations (65)

Trace element partitioning between immiscible silicate melts with H2O, P, S, F, and Cl

Chemical Geology (2013)

Gregory W. Lester T. K. Kyser Abram H. Clark Daniel Layton‐Matthews

Trace element

Melt inclusions

Volatiles

10.1016/j.chemgeo.2013.08.021

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Citations (24)