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J. F. Slack

Publications and source records attributed to J. F. Slack.

At least 19 recordsLinked to original sources
USGS2010

Co-Cu-Au deposits in metasedimentary rocks-A preliminary report

A compilation of data on global Co-Cu-Au deposits in metasedimentary rocks refines previous descriptive models for their occurrence and provides important information for mineral resource assessments and exploration programs. This compilation forms the basis for a new classification of such deposits, which is speculative at this early stage of research. As defined herein, the Co-Cu-Au deposits contain 0.1 percent or more by weight of Co in ore or mineralized rock, comprising disseminated to semi-massive Co-bearing sulfide minerals with associated Fe- and Cu-bearing sulfides, and local gold, concentrated predominantly within rift-related, siliciclastic metasedimentary rocks of Proterozoic age. Some deposits have appreciable Ag ? Bi ? W ? Ni ? Y ? rare earth elements ? U. Deposit geometry includes stratabound and stratiform layers, lenses, and veins, and (or) discordant veins and breccias. The geometry of most deposits is controlled by stratigraphic layering, folds, axial-plane cleavage, shear zones, breccias, or faults. Ore minerals are mainly cobaltite, skutterudite, glaucodot, and chalcopyrite, with minor gold, arsenopyrite, pyrite, pyrrhotite, bismuthinite, and bismuth; some deposits have appreciable tetrahedrite, uraninite, monazite, allanite, xenotime, apatite, scheelite, or molybdenite. Magnetite can be abundant in breccias, veins, or stratabound lenses within ore or surrounding country rocks. Common gangue minerals include quartz, biotite, muscovite, K-feldspar, albite, chlorite, and scapolite; many deposits contain minor to major amounts of tourmaline. Altered wall rocks generally have abundant biotite or albite. Mesoproterozoic metasedimentary successions constitute the predominant geologic setting. Felsic and (or) mafic plutons are spatially associated with many deposits and at some localities may be contemporaneous with, and involved in, ore formation. Geoenvironmental data for the Blackbird mining district in central Idaho indicate that weathering of abundant Fe, S, As, Co, and Cu in sulfide minerals of the deposits produces acidic waters, especially in pyrite-rich deposits; mine runoff has high concentrations of Fe, Cu, and Mn that exceed U.S. drinking water or aquatic life standards.

Open-File Report↗
USGS2008

Mineral chemistry and shrimp U-Pb Geochronology of mesoproterozoic polycrase-titanite veins in the sullivan Pb-Zn-Ag Deposit, British Columbia

Small polycrase-titanite veins 0.1-2 mm thick cut the tourmalinite feeder zone in the deep footwall of the Sullivan Pb-Zn-Ag deposit, southeastern British Columbia. Unaltered, euhedral crystals of polycrase and titanite 50-100 ??m in diameter are variably replaced by a finer-grained alteration-induced assemblage composed of anhedral polycrase and titanite with local calcite, albite, epidote, allanite, and thorite or uranothorite (or both). Average compositions of the unaltered and altered polycrase, as determined by electron-microprobe analysis, are (Y0.38 REE0.49 Th0.10 Ca0.04 Pb0.03 Fe0.01U0.01) (Ti1.48 Nb0.54 W0.04 Ta0.02)O6 and (Y0.42 REE0.32 Th0.15 U0.06 Ca0.04 Pb0.01 Fe0.01) (Ti1.57 Nb0.44 W0.04 Ta0.02)O6, respectively. The unaltered titanite has, in some areas, appreciable F (to 0.15 apfu), Y (to 0.40 apfu), and Nb (to 0.13 apfu). SHRIMP U-Pb geochronology of eight grains of unaltered polycrase yields a weighted 207Pb/206Pb age of 1413 ?? 4 Ma (2??) that is interpreted to be the age of vein formation. This age is 50-60 m.y. younger than the ca. 1470 Ma age of synsedimentary Pb-Zn-Ag mineralization in the Sullivan deposit, which is based on combined geological and geochronological data. SHRIMP ages for altered polycrase and titanite suggest later growth of minerals during the ???1370-1320 Ma East Kootenay and ???1150-1050 Ma Grenvillian orogenies. The 1413 ?? 4 Ma age for the unaltered polycrase in the veins records a previously unrecognized post-ore (<1470 Ma) and premetamorphic (>1370 Ma) mineralizing event in the Sullivan deposit and vicinity. The SHRIMP U-Pb age of the polycrase and high concentrations of REE, Y, Ti, Nb, and Th in the veins, together with elevated F in titanite and the absence of associated sulfides, suggest transport of these high-field-strength elements (HFSE) by F-rich and S-poor hydrothermal fluids unrelated to the fluids that formed the older Fe-Pb-Zn-Ag sulfide ores of the Sullivan deposit. Fluids containing abundant REE, HFSE, and F may have been derived from a geochemically specialized magma such as those that form alkaline granites, pegmatites, or carbonatites. In an alternative model. preferred here, these fluids were associated with a rift-related, crustal metasomatic event in the region. Determination of a Mesoproterozoic age for the polycrase-titanite veins establishes the first known occurrence of pre-Grenvillian REE-rich mineralization in the Belt-Purcell basin.

Canadian Mineralogist↗
USGS2007

Suboxic deep seawater in the late Paleoproterozoic: Evidence from hematitic chert and iron formation related to seafloor-hydrothermal sulfide deposits, central Arizona, USA

A current model for the evolution of Proterozoic deep seawater composition involves a change from anoxic sulfide-free to sulfidic conditions 1.8??Ga. In an earlier model the deep ocean became oxic at that time. Both models are based on the secular distribution of banded iron formation (BIF) in shallow marine sequences. We here present a new model based on rare earth elements, especially redox-sensitive Ce, in hydrothermal silica-iron oxide sediments from deeper-water, open-marine settings related to volcanogenic massive sulfide (VMS) deposits. In contrast to Archean, Paleozoic, and modern hydrothermal iron oxide sediments, 1.74 to 1.71??Ga hematitic chert (jasper) and iron formation in central Arizona, USA, show moderate positive to small negative Ce anomalies, suggesting that the redox state of the deep ocean then was at a transitional, suboxic state with low concentrations of dissolved O2 but no H2S. The presence of jasper and/or iron formation related to VMS deposits in other volcanosedimentary sequences ca. 1.79-1.69??Ga, 1.40??Ga, and 1.24??Ga also reflects oxygenated and not sulfidic deep ocean waters during these time periods. Suboxic conditions in the deep ocean are consistent with the lack of shallow-marine BIF ??? 1.8 to 0.8??Ga, and likely limited nutrient concentrations in seawater and, consequently, may have constrained biological evolution. ?? 2006 Elsevier B.V. All rights reserved.

Earth and Planetary Science Letters↗
USGS2006

High REE and Y concentrations in Co-Cu-Au ores of the Blackbird district, Idaho

Analysis of 11 samples of strata-bound Co-Cu-Au ore from the Blackbird district in Idaho shows previously unknown high concentrations of rare earth elements (REE) and Y, averaging 0.53 wt percent ???REE + Y oxides. Scanning electron microscopy indicates REE and Y residence in monazite, xenotime, and allanite that form complex intergrowths with cobaltite, suggesting coeval Co and REE + Y mineralization during the Mesoproterozoic. Occurrence of high REE and Y concentrations in the Blackbird ores, together with previously documented saline-rich fluid inclusions and Cl-rich biotite, suggest that these are not volcanogenic massive sulfide or sedimentary exhalative deposits but instead are iron oxide-copper-gold (IOCG) deposits. Other strata-bound Co deposits of Proterozoic age in the North American Cordillera and elsewhere in the world may have potential for REE and Y resources. IOCG deposits with abundant light REE should also be evaluated for possible unrecognized heavy REE and Y mineralization. ?? 2006 by Economic Geology.

Economic Geology↗
USGS2004

Textural, compositional, and sulfur isotope variations of sulfide minerals in the Red Dog Zn-Pb-Ag deposits, Brooks Range, Alaska: Implications for Ore Formation

The Red Dog Zn-Pb deposits are hosted in organic-rich mudstone and shale of the Mississippian Kuna Formation. A complex mineralization history is defined by four sphalerite types or stages: (1) early brown sphalerite, (2) yellow-brown sphalerite, (3) red-brown sphalerite, and (4) late tan sphalerite. Stages 2 and 3 constitute the main ore-forming event and are volumetrically the most important. Sulfides in stages 1 and 2 were deposited with barite, whereas stage 3 largely replaces barite. Distinct chemical differences exist among the different stages of sphalerite. From early brown sphalerite to later yellow-brown sphalerite and red-brown sphalerite, Fe and Co content generally increase and Mn and Tl content generally decrease. Early brown sphalerite contains no more than 1.9 wt percent Fe and 63 ppm Co, with high Mn (up to 37 ppm) and Tl (126 ppm), whereas yellow-brown sphalerite and red-brown sphalerite contain high Fe (up to 7.3 wt %) and Co (up to 382 ppm), and low Mn (<27 ppm) and Tl (<37 ppm). Late tan sphalerite has distinctly lower Fe (< 0.9 wt %) and higher Tl (up to 355 ppm), Mn (up to 177 ppm), and Ge (426 ppm), relative to earlier sphalerite. Wide ranges in concentrations of Ag, Cu, Pb, and Sb characterize all sphalerite types, particularly yellow-brown sphalerite and red-brown sphalerite, and most likely reflect submicroscopic inclusions of galena, chalcopyrite and/or tetrahedrite in the sphalerite. In situ ion microprobe sulfur isotope analyses show a progression from extremely low ??34S values for stage 1 (as low as -37.20???) to much higher values for yellow-brown sphalerite (mean of 3.3???; n = 30) and red-brown sphalerite (mean of 3.4; n = 20). Late tan sphalerite is isotopically light (-16.4 to -27.2???). The textural, chem ical, and isotopic data indicate the following paragenesis: (1) deposition of early brown sphalerite with abundant barite, minor pyrite, and trace galena immediately beneath the sea floor in unconsolidated mud; (2) deposition of yellow-brown sphalerite during subsea-floor hydrothermal recrystallization and coarsening of preexisting barite; (3) open-space deposition of barite, red-brown sphalerite and other sulfides in veins and coeval replacement of barite; and (4) postore sulfide deposition, including the formation of late tan sphalerite breccias. Stage 1 mineralization took place in a low-temperature environment where fluids rich in Ba mixed with pore water or water-column sulfate to form barite, and metals combined with H2S derived from bacterial sulfate reduction to form sulfides. Higher temperatures and salinities and relatively oxidized ore-stage fluids (stages 2 and 3) compared with stage 1 were probably important controls on the abundances and relative amounts of metals in the fluids and the resulting sulfide chemistry. Textural observations and isotopic data show that preexisting barite was reductively dissolved, providing a source of H2S for sulfide mineral formation. In stage 3, the continued flow of hydrothermal fluids caused thermal alteration of organic-rich mudstones and a build-up of methane that led to fluid overpressuring, hydrofracturing, and vein formation. Barite, red-brown sphalerite, and other sulfides were deposited in the veins, and preexisting barite was pervasively replaced by red-brown sphalerite. Hydrothermal activity ceased until Jurassic time when thrusting and large-scale fluid flow related to the Brookian orogeny remobilized and formed late tan sphalerite in tectonic breccias. ?? 2004 by Economic Geology.

Economic Geology↗
USGS2000

Geochronology and geology of late Oligocene through Miocene volcanism and mineralization in the western San Juan Mountains, Colorado

Twenty-five new 40Ar/39Ar ages from volcanic rocks and veins in the western San Juan Mountains clarify relationships between volcanism and mineralization in this classic area. Five calc-alkaline ash-flow sheets erupted from caldera sources (Ute Ridge, Blue Mesa, Dillon Mesa, Sapinero Mesa, and Crystal Lake Tuffs) from 28.6 to 27.6 Ma. This is a much more restricted time interval than previously thought and indicates that the underlying batholith rose and evolved very rapidly beneath the western San Juan Mountains. The new ages and geologic relations constrain the timing of joint resurgence of the Uncompahgre and San Juan calderas to between 28.2 and 27.6 Ma. The collapse of the Silverton caldera produced a set of strong ring fractures that intersected with graben faults on the earlier resurgent dome to produce the complex set of structures that localized the mid-Miocene epithermal gold veins. Later calc-alkaline monzonitic to quartz monzontic plutons solidified at 26.5-26.0 Ma as the underlying batholith rose through its volcanic cover. A new age from lavas near Uncompahgre Peak supports earlier interpretations that these lavas were fed by nearby 26 Ma monzonite intrusions. Nearly all of these intrusions are associated with subeconomic Mo and Cu mineralization and associated alteration, and new ages of 26.40 and 25.29 Ma from the Ute-Ulay and Lilly veins in the Lake City region show that some of the most important silver and base-metal veins were temporally and possibly genetically connected to these plutons. In addition, the Golden Fleece telluride vein cuts all of the post-Uncompahgre caldera volcanics in the area and is probably temporally related to this cycle, though its age of 27.5 ? 0.3 Ma was determined by less precise U/Pb methods. The 22.9 Ma Lake City caldera collapsed within the older Uncompahgre caldera structure but is petrologically unrelated to the older calc-alkaline activity. The distinctive suite of high-silica rhyolite tuff and alkaline resurgent intrusions indicates that it is closely related to the early stages of bimodal high-silica rhyolite-alkali basalt volcanism that accompanied the onset of extensional tectonism in the region. Both 40Ar/39Ar ages and paleomagnetic data confirm that the entire caldera sequence formed in less than 330,000 years. Only weak quartz vein mineralization is present in the center of the caldera, and it appears to be related to leaching of metals from the intracaldera tuffs above the resurgent intrusion. Massive alunitization and weak Mo and Cu mineralization along the eastern ring fracture are associated with calc-alkaline lavas and stocks related to late stages of the caldera cycle. These calc-alkaline stocks also appear to be genetically and temporally linked to a radial pattern of barite-precious metal veins on the northeastern margin of the Lake City caldera.

Colorado↗
USGS1999

Boron isotope systematics of tourmaline formation in the Sullivan Pb-Zn-Ag deposit, British Columbia, Canada

We report here the results of 54 boron isotope analyses of tourmaline associated with the giant Sullivan Pb-Zn-Ag deposit in southeastern British Columbia, Canada. The ??11B values range from -11.1 to -2.9???, which is almost as great as the range found worldwide in tourmalines from 33 massive sulfide deposits and tourmalinites in dominantly clastic metasedimentary terranes. The major control on the overall ??11B values of the Sullivan tourmalinites is the boron source. Potential controls over the large range of the data also include: (1) differences in formation temperatures of the tourmalinites, (2) different stages of tourmaline formation, (3) variations in the proportions of dissolved boron incorporated into the tourmaline (Rayleigh fractionation), (4) seawater entrainment, and (5) post-depositional metamorphism. The boron isotope data at Sullivan are consistent with boron derivation from leaching of footwall clastic sediments. However, the great abundance of tourmaline in the Sullivan deposit suggests that the local clastic sediments were not the sole source of boron, and we argue that non-marine evaporites, buried deep below the orebody, are the most viable source of this additional boron. It is likely that some of the variation in tourmaline ??11B values reflect mixing of boron from these two sources. Comparison of the potential effects of these controls with geologic and other geochemical evidence suggests that major causes for the wide range of ??11B values measured at Sullivan are seawater entrainment and Rayleigh fractionation, although in places, post-depositional alteration and thermal metamorphism were important in determining ??11B values of some of the recrystallized tourmalinites.

Chemical Geology↗
USGS1998

Boron-rich mud volcanoes of the Black Sea region: Modern analogues to ancient sea-floor tourmalinites associated with Sullivan-type Pb-Zn deposits?

Large submarine mud volcanoes in the abyssal part of the Black Sea south of the Crimean Peninsula are similar in many respects to synsedimentary mud volcanoes in the Mesoproterozoic Belt-Purcell basin. One of the Belt-Purcell mud volcanoes directly underlies the giant Sullivan Pb-Zn-Ag deposit in southeastern British Columbia. Footwall rocks to the Sullivan deposit comprise variably tourmalinized siltstone, conglomerate, and related fragmental rock; local thin pyrrhotite-rich and spessartine-quartz beds are interpreted as Fe and Fe-Mn exhalites, respectively. Analogous Fe- and Mn-rich sediments occur near the abyssal Black Sea mud volcanoes. Massive pyrite crusts and associated carbonate chimneys discovered in relatively shallow waters (∼200 m depth) west of the Crimean Peninsula indicate an active sea-floor–hydrothermal system. Subaerial mud volcanoes on the Kerch and Taman Peninsulas (∼100 km north of the abyssal mud volcanoes) contain saline thermal waters that locally have very high B contents (to 915 mg/L). These data suggest that tourmalinites might be forming in or near submarine Black Sea mud volcanoes, where potential may also exist for Sullivan-type Pb-Zn mineralization.

Geology↗
USGS1996

Mn-rich ilmenite from the Sullivan Pb-Zn-Ag deposit, British Columbia

Electron-microprobe analyses of 76 ilmenite grains from 13 locations in the footwall, hanging wall, and ore zone of the Sullivan Pb-Zn-Ag deposit, Kimberley, British Columbia, and from regionally developed tourmalinite of the Middle Proterozoic Aldridge Formation show two different modes that reflect two stages of formation. The first stage of ilmenite formation occurred as a result of greenschist-facies regional metamorphism, which also produced the associated Mn-rich garnet. Ilmenite from this stage forms inclusions within garnet and has a relatively low Mn content (<5.5 wt% MnO), owing to the preferential partitioning of Mn into the garnet. A second metamorphic or hydrothermal event resulted in the formation of ilmenite-bearing veinlets (+ chlorite + quartz + sulfides) that cut garnet and associated biotite. This latter type of ilmenite has a higher Mn content (up to 16.7 wt% MnO) that reflects remobilization of Mn within the local environment. Both types of Mn-rich ilmenite are considered to be derived from Mn originally concentrated in pools of dense brine that formed during synsedimentary, submarine-exhalative mineralization.

Canadian Mineralogist↗
USGS1996

Feruvite from the Sullivan Pb-Zn-Ag deposit, British Columbia

Feruvite, an uncommon Ca- and Fe2+-rich tourmaline species, has been discovered in the footwall of the Sullivan Pb-Zn-Ag deposit (British Columbia) near gabbro sills and dikes. Its chemical composition varies according to occurrence: feruvite from the shallow footwall has lower Ca, higher Al, and higher X-site vacancies than that from the deep footwall. The major chemical substitution involved in the feruvite is the exchange vector CaMgO???-1Al-1(OH)-1. The most important factor controlling feruvite formation at Sullivan is likely the reaction of Fe-rich hydrothermal fluids with Ca-rich minerals in gabbro and host rocks. This reaction led to the breakdown of Ca-rich minerals (plagioclase and hornblende), with release of Ca to solution and its incorporation into feruvite. This process probably postdated the main stages of formation of fine-grained, intermediate schorl-dravite in the tourmalinite pipe in the footwall, and is attributed to postore intrusion of gabbro and associated albite-chlorite-pyrite alteration.

Canadian Mineralogist↗
USGS1994

Clastic metasediments of the Early Proterozoic Broken Hill Group, New South Wales, Australia: Geochemistry, provenance, and metallogenic significance

Whole-rock analyses of samples of pelite, psammite, and psammopelite from the Early Proterozoic Broken Hill Group (Willyama Supergroup) in the Broken Hill Block, New South Wales, Australia, reveal distinctive geochemical signatures. Major-element data show high Al 2 O 3 and K 2 O, low MgO and Na 2 O, and relatively high Fe 2 O 3 T MgO "> Fe2O3TMgO ratios, compared to average Early Proterozoic clastic metasediments. High field strength elements (HFSE) are especially abundant, including Nb (most 15–27 ppm), Ta (most 1.0–2.2 ppm), Th (17–36 ppm), Hf (4–15 ppm), and Zr (most 170–400 ppm); Y (33–74 ppm) is also high. Concentrations of ferromagnesian elements are generally low ( Sc = < 20 ppm, Ni = ≤ 62 ppm, Co = <26 ppm; Cr = most < 100 ppm). Data for rare earth elements (REEs) show high abundances of light REEs ( La CN = 116–250 × chondrite; La CN = 437 in one sample), high La CN Yb CN "> LaCNYbCN ratios (5.6–13.9), and large negative Eu anomalies ( Eu Eu &#x2217; = 0.32&#x2013;0.57 "> EuEu∗= 0.32–0.57 ). The geochemical data indicate derivation of the metasedimentary rocks of the Broken Hill Group by the erosion mainly of felsic igneous (or meta-igneous) rocks. High concentrations of HFSE, Y, and REEs in the metasediments suggest a provenance dominanted by anorogenic granites and(or) rhyolites, including those with A-type chemistry. Likely sources of the metasediments were the rhyolitic to rhyodacitic protoliths of local quartz + feldspar ± biotite ± garnet gneisses (e.g., Potosi-type gneiss) that occur within the lower part of the Willyama Supergroup, or chemically similar basement rocks in the region; alternative sources may have included Early Proterozoic anorogenic granites and(or) rhyolites in the Mount Isa and(or) Pine Creek Blocks of northern Australia, or in the Gawler craton of South Australia. Metallogenic considerations suggest that the metasediments of the Broken Hill Block formed enriched source rocks during the generation of pegmatite-hosted deposits and concentrations of La, Ce, Nb, Ta, Th, and Sn in the region. Li, Be, B, W, and U in pegmatite minerals of the district may have been acquired during granulite-facies metamorphism of the local metasediments.

New South Wales↗
USGS1993

Origin and significance of tourmaline-rich rocks in the Broken Hill district, Australia

Tourmaline-rich rocks are widespread minor lithologies within the Early Proterozoic Willyama Supergroup in the Broken Hill district, Australia. Tourmaline concentrations occur in strata-bound and local stratiform tourmalinites, clastic metasedimentary rocks, quartz-gahnite lode rocks, stratiform Pb-Zn-Ag sulfide ores, garnet quartzites, strata-bound scheelite deposits, quartz-tourmaline nodules, discordant quartz veins, and granitic pegmatites. Most of the tourmaline-rich rocks are within the Broken Hill Group that hosts the main Pb-Zn-Ag ores.At the Globe mine along the northeast end of the main lodes, tourmalinites are closely associated with Pb-Zn-Ag mineralization and in places are interbedded with Mn-rich garnet quartzites. Galena and other ore minerals occur locally in the cores of recrystallized tourmaline grains in these tourmalinites, indicating that tourmaline and sulfides were present together prior to deformation and high-grade metamorphism. Electron microprobe analyses of tourmalines intergrown with Fe sulfides at the Globe mine show Mg-rich compositions relative to tourmalines in sulfide-free assemblages from the same area, suggesting early (premetamorphic) introduction of boron and Mg enrichment of tourmaline by sulfide-silicate reactions during metamorphism.Combined field and geochemical data indicate that the district tourmalinites represent normal clastic sediments that were metasomatically altered by boron-rich hydrothermal fluids at or below the sediment-water interface. Whole-rock chemical analyses of 33 tourmaline-rich rocks show linear trends of data for major and trace elements that closely resemble the trends observed for unmineralized elastic metasedimentary rocks of the district. Average Fe/Al, Mg/Al, Na/Al, and Ti/Al molar ratios of the tourmaline-rich rocks and clastic metasediments are very similar; the average K/Al molar ratio of the tourmaline-rich rocks is significantly lower than that of the clastic metasediments, reflecting the loss of K during tourmalinite formation. Chondrite-normalized patterns of rare earth elements (REE) in the quartz-rich tourmalinites are generally similar to those of the clastic metasediments, except for minor depletions of light REE; local positive and negative Ce anomalies suggest tourmalinite formation in the presence of seawater or a seawater-derived pore fluid. The geochemical data imply relative immobility of Al, Ti, Cr, and heavy REE during hydrothermal alteration and later metamorphism. Boron isotope analyses of 52 tourmaline separates show a total range of delta 11 B values from -26.8 to -17.0 per mil. Fine-grained, euhedral, nonpoikilitic tourmalines from tourmalinites in the andalusite-muscovite zone in the northern part of the district (e.g., Black Prince mine) have delta 11 B values from -21 to -17 per mil, whereas coarse granoblastic and poikilo-blastic tourmalines from the sillimanite and two-pyroxene granulite zones in the southern part of the district (e.g., Globe mine) have delta 11 B values of-24 to -19 per mil. Tourmalines in strongly retrogressed tourmalinites have delta 11 B values from about -27 to -20 per mil. The observed variations in delta 11 B are consistent with prograde and retrograde metamorphic fractionation of boron isotopes, in which the fluid phase is preferentially enriched in the heavier isotope ( 11 B). Premetamorphic hydrothermal fluids that deposited the Black Prince tourmalinites had delta 11 B values of-8 to -5 per mil at 200 degrees to 300 degrees C, suggesting a boron source from nonmarine evaporite borates.Tourmalinites in the Broken Hill district apparently formed by the same submarine hydrothermal processes as the main Pb-Zn-Ag lodes and the siliceous ferromanganese protoliths of the garnet quartzites. In our model, the hydrothermal system(s) acquired abundant boron by leaching evaporitic borates within the Thackaringa Group, the stratigraphic sequence that underlies the Broken Hill Group and most of the tourmaline concentrations. We suggest that evaporites of the Thackaringa Group provided a source of readily extractable boron for formation of the tourmalinites and also the source of the fluoride, sulfur, and perhaps the carbonate in the main lodes; such evaporites may have been critical for increased metal chloride complexing and transport necessary for deposition of the high-grade Pb-Zn-Ag ores. The Broken Hill deposit may have formed contemporaneously with the Mount Isa and McArthur River Pb-Zn-Ag deposits in similar evaporite-bearing sequences during widespread Early Proterozoic continental rifting.

Economic Geology↗
USGS1992

Hydrothermal and metamorphic berthierine from the Kidd Creek volcanogenic massive sulfide deposit, Timmins, Ontario

Berthierine, a 7 A?? Fe-Al member of the serpentine group, occurs in the footwall stringer zone of the Archean Kidd Creek massive sulfide deposit, associated with quartz, muscovite, chlorite, pyrite, sphalerite, chalcopyrite, and local tourmaline, cassiterite, and halloysite. Petrographic and scanning electron microscopic (SEM) studies reveal different types of berthierine occurrences, including interlayers within the rims on deformed chlorite, intergrowths with muscovite and halloysite, and discrete coarse grains. This is the first reported occurrence of berthierine from volcanogenic massive sulfide deposits. Textural relations suggest that most of the berthierine formed as a primary hydrothermal mineral at relatively high temperatures (~350??C) in the footwall stringer zone, probably by the replacement of a pre-existing aluminous phase such as muscovite or chlorite. However, the intergrowth textures observed by SEM and TEM suggest that some of the berthierine originated by syn- or post-metamorphic replacement of chlorite. -from Authors

Canadian Mineralogist↗
USGS1991

Boron analysis by electron microprobe using MoB4C layered synthetic crystals

Preliminary electron microprobe studies of B distribution in minerals have been carried out using MoB4C-layered synthetic crystals to improve analytical sensitivity for B. Any microprobe measurements of the B contents of minerals using this crystal must include analyses for Cl to assess and correct for the interference of Cl X-rays on the BK?? peak. Microprobe analyses for B can be made routinely in tourmaline and other B-rich minerals, and minor B contents also can be determined in common rock-forming minerals. Incorporation of unusually high B contents in minerals other than borosilicates has been discovered in prograde and retrograde minerals in tourmalinites from the Broken Hill district, Australia, and may reflect high B activities produced during the metamorphism of tourmaline-rich rocks. -from Authors

American Mineralogist↗
USGS1989

Boron isotopic composition of tourmaline from massive sulfide deposits and tourmalinites

Boron isotope ratios (11B/10B) have been measured on 60 tourmaline separates from over 40 massive sulfide deposits and tourmalinites from a variety of geologic and tectonic settings. The coverage of these localities is global (5 continents) and includes the giant ore bodies at Kidd Creek and Sullivan (Canada), Broken Hill (Australia), and Ducktown (USA). Overall, the tourmalines display a wide range in ??11B values from -22.8 to +18.3??? Possible controls over the boron isotopic composition of the tourmalines include: 1) composition of the boron source, 2) regional metamorphism, 3) water/rock ratios, 4) seawater entrainment, 5) temperature of formation, and 6) secular variations in seawater ??11B. The most significant control appears to be the composition of the boron source, particularly the nature of footwall lithologies; variations in water/ rock ratios and seawater entrainment are of secondary importance. The boron isotope values seem especially sensitive to the presence of evaporites (marine and non-marine) and carbonates in source rocks to the massive sulfide deposits and tourmalinites. ?? 1989 Springer-Verlag.

Contributions to Mineralogy and Petrology↗
USGS1989

Boron isotope evidence for the involvement of non-marine evaporites in the origin of the Broken Hill ore deposits

Identifying the palaeogeographic setting and mode of origin of stratabound ore deposits can be difficult in high-grade metamorphic terranes, where the effects of metamorphism may obscure the nature of the protoliths. Here we report boron isotope data for tourmalines from the early Proterozoic Broken Hill block, in Australia, which hosts giant lead-zinc-silver sulphide deposits. With one exception the 11 B/ 10 B ratios are lower than those for all other tourmalines from massive sulphide deposits and tour-malinites elsewhere in the world. We propose that these low ratios reflect leaching of boron from non-marine evaporitic borates by convecting hydrothermal fluids associated with early Proterozoic continental rifting. A possible modern analogue is the Salton Sea geothermal field in California.

Nature↗