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John F. Slack

Publications and source records attributed to John F. Slack.

At least 55 records · Page 3Linked to original sources
USGS2009

A New Occurrence Model for National Assessment of Undiscovered Volcanogenic Massive Sulfide Deposits

Volcanogenic massive sulfide (VMS) deposits are very significant current and historical resources of Cu-Pb-Zn-Au-Ag, are active exploration targets in several areas of the United States and potentially have significant environmental effects. This new USGS VMS deposit model provides a comprehensive review of deposit occurrence and ore genesis, and fully integrates recent advances in the understanding of active seafloor VMS-forming environments, and integrates consideration of geoenvironmental consequences of mining VMS deposits. Because VMS deposits exhibit a broad range of geological and geochemical characteristics, a suitable classification system is required to incorporate these variations into the mineral deposit model. We classify VMS deposits based on compositional variations in volcanic and sedimentary host rocks. The advantage of the classification method is that it provides a closer linkage between tectonic setting and lithostratigraphic assemblages, and an increased predictive capability during field-based studies.

Open-File Report↗
USGS2009

Mesozoic magmatism and base-metal mineralization in the Fortymile mining district, eastern Alaska — Initial results of petrographic, geochemical, and isotopic studies in the Mount Veta area

We present here the initial results of a petrographic, geochemical, and isotopic study of Mesozoic intrusive rocks and spatially associated Zn-Pb-Ag-Cu-Au prospects in the Fortymile mining district in the southern Eagle quadrangle, Alaska. Analyzed samples include mineralized and unmineralized drill core from 2006 and 2007 exploration by Full Metal Minerals, USA, Inc., at the Little Whiteman (LWM) and Fish prospects, and other mineralized and plutonic samples collected within the mining district is part of the USGS study. Three new ion microprobe U-Pb zircon ages are: 210 ± 3 Ma for quartz diorite from LWM, 187 ± 3 Ma for quartz monzonite from Fish, and 70.5 ± 1.1 Ma for altered rhyolite porphyry from Fish. We also present 11 published and unpublished Mesozoic thermal ionization mass spectrometric U-Pb zircon and titanite ages and whole-rock geochemical data for the Mesozoic plutonic rocks. Late Triassic and Early Jurassic plutons generally have intermediate compositions and are slightly foliated, consistent with synkinematic intrusion. Several Early Jurassic plutons contain magmatic epidote, indicating emplacement of the host plutons at mesozonal crustal depths of greater than 15 km. Trace-element geochemical data indicate an arc origin for the granitoids, with an increase in the crustal component with time. Preliminary study of drill core from the LWM Zn-Pb-Cu-Ag prospect supports a carbonate-replacement model of mineralization. LWM massive sulfides consist of sphalerite, galena, and minor pyrite and chalcopyrite, in a gangue of calcite and lesser quartz; silver resides in Sb-As-Ag sulfosalts and pyrargyrite, and probably in submicroscopic inclusions within galena. Whole-rock analyses of LWM drill cores also show elevated In, an important metal in high-technology products. Hypogene mineralized rocks at Fish, below the secondary Zn-rich zone, are associated with a carbonate host and also may be of replacement origin, or alternatively, may be a magnetite-bearing Zn skarn. Cu-Zn-Pb-Ag-Au showings at the Oscar pros-pect occur in marble-hosted magnetite and pyrrhotite skarn that is spatially related to the stocks, dikes, and sills of the Early Jurassic syenite of Mount Veta. Mineralized rocks at the Eva Creek Ag-Zn-Pb-Cu prospect are within 1.5 km of the Mount Veta pluton, which is epidotized and locally altered along its contact with metamorphosed country rock east of the prospect. We report five new sulfide Pb-isotopic analyses from the LWM, Oscar, and Eva Creek prospects and compare these sulfide Pb-isotopic ratios with those for sulfides from nearby deposits and prospects in the Yukon-Tanana Upland and with feldspar Pb-isotopic ratios for Mesozoic plutons in the region. Disparities between the Pb-isotopic ratios for sulfides and igneous feldspars are consistent with a carbonate-replacement model for both the LWM and Eva Creek prospects. The presence in the Fortymile district of base-metal sulfides within both calc-silicate-rich skarns and the calc-silicate-free carbonate replacement deposits may reflect multistage mineralization by magmatic-hydrothermal systems during the emplacement of two or more magmatically unrelated igneous intrusions. Alternatively, all of the mineralized occurrences could be products of one regionally zoned system that formed during the intrusion of a single pluton. In addition to the likely origin of some of the base-metal occurrences by intrusion-related hydrothermal fluids, proximity of the LWM prospect to the northeast-striking, high-angle Kechumstuk Fault suggests that fluid flow along the fault also played an important role during carbonate-replacement mineralization.

Alaska↗
USGS2007

Regional Fluid Flow and Basin Modeling in Northern Alaska

The foothills of the Brooks Range contain an enormous accumulation of zinc (Zn) in the form of zinc sulfide and barium (Ba) in the form of barite in Carboniferous shale, chert, and mudstone. Most of the resources and reserves of Zn occur in the Red Dog deposit and others in the Red Dog district; these resources and reserves surpass those of most deposits worldwide in terms of size and grade. In addition to zinc and lead sulfides (which contain silver, Ag) and barite, correlative strata host phosphate deposits. Furthermore, prolific hydrocarbon source rocks of Carboniferous and Triassic to Early Jurassic age generated considerable amounts of petroleum that may have contributed to the world-class petroleum resources of the North Slope. Deposits of Zn-Pb-Ag or barite as large as those in the Brooks Range are very rare on a global basis and, accordingly, multiple coincident favorable factors must be invoked to explain their origins. To improve our understanding of these factors and to contribute to more effective assessments of resources in sedimentary basins of northern Alaska and throughout the world, the Mineral Resources Program and the Energy Resources Program of the U.S. Geological Survey (USGS) initiated a project that was aimed at understanding the petroleum maturation and mineralization history of parts of the Brooks Range that were previously poorly characterized. The project, titled “Regional Fluid Flow and Basin Modeling in Northern Alaska,” was undertaken in collaboration with industry, academia, and other government agencies. This Circular contains papers that describe the results of the recently completed project. The studies that are highlighted in these papers have led to a better understanding of the following: The complex sedimentary facies relationships and depositional settings and the geochemistry of the sedimentary rocks that host the deposits (sections 2 and 3). The factors responsible for formation of the barite and zinc deposits (sections 4 and 5). The geochemical indicators or exploration tools that might be used to locate other large deposits of similar character in the Red Dog district and elsewhere (section 6). The isotopic compositions of barite and sulfide deposits (sections 7 and 8) The distribution and nature of phosphate and metalliferous oil shale localities (sections 9 and 10). The architecture, kinematics, and timing of the complex thrust systems that disrupted and redistributed the Carboniferous and younger rocks; these studies are necessary in order to make a realistic palinspastic reconstruction of the basin (sections 11 and 12). The nature and extent of the petroleum system sourced from Mississippian rocks (section 13).

Circular↗
USGS2007

Geochemical and sulfur-isotopic signatures of volcanogenic massive sulfide deposits on Prince of Wales Island and vicinity, southeastern Alaska

Stratabound volcanogenic massive sulfide (VMS) deposits on Prince of Wales Island and vicinity, southeastern Alaska, occur in two volcanosedimentary sequences of Late Proterozoic through Cambrian and of Ordovician through Early Silurian age. This study presents geochemical data on sulfide-rich samples, in situ laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) of sulfide minerals, and sulfur-isotopic analyses of sulfides and sulfates (barite) for identifying and distinguishing between primary sea-floor signatures and later regional metamorphic overprints. These datasets are also used here in an attempt to discriminate the VMS deposits in the older Wales Group from those in the younger Moira Sound unit (new informal name). The Wales Group and its contained VMS deposits have been multiply deformed and metamorphosed from greenschist to amphibolite grade, whereas the Moira Sound unit and related VMS deposits are less deformed and generally less metamorphosed (lower to middle greenschist grade). Variations in the sulfide mineral assemblages and textures of the VMS deposits in both sequences reflect a combination of processes, including primary sea-floor mineralization and sub-sea-floor zone refining, followed by metamorphic recrystallization. Very coarse grained (>1 cm diam) sulfide minerals and abundant pyrrhotite are restricted to VMS deposits in a small area of the Wales Group, at Khayyam and Stumble-On, which record high-grade metamorphism of the sulfides. Geochemical and sulfur-isotopic data distinguish the VMS deposits in the Wales Group from those in the Moira Sound unit. Although base- and precious-metal contents vary widely in sulfide-rich samples from both sequences, samples from the Moira Sound generally have proportionately higher Ag contents relative to base metals and Au. In situ LA-ICP-MS analysis of trace elements in the sulfide minerals suggests that primary sea-floor hydrothermal signatures are preserved in some samples (for example, Mn, As, Sb, and Tl in pyrite from the Moira Sound unit), whereas in other samples the signatures are varyingly annealed, owing to metamorphic overprinting. A limited LA-ICP-MS database for sphalerite indicates that low-Fe sphalerite is preferentially associated with the most Au rich deposits, the Niblack and Nutkwa. Sulfur-isotopic values for sulfide minerals in the VMS deposits in the Wales Group range from 5.9 to 17.4 permil (avg 11.5?2.7 permil), about 5 to 6 permil higher than those in the Moira Sound unit, which range from -2.8 to 10.4 permil (avg 6.1?4.0 permil). This difference in 34Ssulfide values reflects a dominantly seawater sulfate source of the sulfides and is linked to the 34S values of contemporaneous seawater sulfate, which were slightly higher during the Late Proterozoic through Cambrian than during the Ordovician through Early Silurian.

Alaska↗
USGS2005

Geochemistry and jasper beds from the Ordovician Løkken ophiolite, Norway: origin of proximal and distal siliceous exhalites

Stratiform beds of jasper (hematitic chert), composed essentially of SiO 2 (69–95 wt %) and Fe 2 O 3 (3–25 wt %), can be traced several kilometers along strike in the Ordovician Løkken ophiolite, Norway. These siliceous beds are closely associated with volcanogenic massive sulfide (VMS) deposits and are interpreted as sea-floor gels that were deposited by fallout from hydrothermal plumes in silica-rich seawater, in which plume-derived Fe oxyhydroxide particles promoted flocculation and rapid settling of large (~200 μm) colloidal particles of silica-iron oxyhydroxide. Concentrations of chalcophile elements in the jasper beds are at the parts per million level implying that sulfide particle fallout was insignificant and that the Si-Fe gel-forming plumes were mainly derived from intermediate- (100°–250°C) to high-temperature (>250°C) white smoker-type vents with high Fe/S ratios. The interpreted setting is similar to that of the Lau basin, where high-temperature (280°–334°C) white smoker venting alternates or overlaps with sulfide mound-forming black smoker venting. Ratios of Al, Sc, Th, Hf, and REE to iron are very low and show that the detrital input was <0.1 percent of the bulk jasper. Most jasper beds are enriched in U, V, P, and Mo relative to the North American Shale Composite, reflecting a predominantly seawater source, whereas REE distribution patterns (positive Eu and negative Ce anomalies) reflect variable mixing of hydrothermal solutions with oxic seawater at dilution ratios of ~10 2 to 10 4 . Trace element variations in the gel precursor to the jasper are thought to have been controlled by coprecipitation and/or adsorption by Fe oxyhydroxide particles that formed by the oxidation of hydrothermal Fe 2+ within the variably seawater-diluted hydrothermal plume(s). Thick jasper layers near the Høydal VMS orebody show distinct positive As/Fe and Sb/Fe anomalies that are attributed to near-vent rapid settling of Si-Fe particles derived from As- and Sb-rich hydrothermal fluids prior to extensive mixing with seawater in the buoyant plume. Particles that formed later in the highly diluted nonbuoyant plume formed relatively As and Sb poor distal jasper. The large particle sizes and accordingly high settling rates of the particles, together with mass-balance calculations based on modern vent field data, suggest that individual meter-thick jasper beds formed within a plume lifetime of 200 years or less. The lack of thick jasper beds near the Løkken VMS orebody, which is larger than the Høydal orebody by more than two orders of magnitude, probably reflects a shift to anoxic conditions during Løkken mineralization. This environment limited oxidation of iron in the hydrothermal plume and formation of the ferric oxyhydroxides necessary for the flocculation of silica and sea-floor deposition of the gel precursor of the jasper beds. Distal pyritic and iron-poor cherts are more common than jasper in ancient VMS-hosting sequences. The origin of these other types of siliceous exhalite is enigmatic but at least in some cases involved sulfidation, reduction to magnetite, or dissolution of the original ferric iron in precursor Si-rich gels, either by hydrothermal or diagenetic processes.

Economic Geology↗
USGS2005

Oceanic Pb-isotopic sources of Proterozoic and Paleozoic volcanogenic massive sulfide deposits on Prince of Wales Island and vicinity, southeastern Alaska

Volcanogenic massive sulfide (VMS) deposits on Prince of Wales Island and vicinity in southeastern Alaska are associated with Late Proterozoic through Cambrian volcanosedimentary rocks of the Wales Group and with Ordovician through Early Silurian felsic volcanic rocks of the Moira Sound unit (new informal name). The massive sulfide deposits in the Wales Group include the Big Harbor, Copper City, Corbin, Keete Inlet, Khayyam, Ruby Tuesday, and Stumble-On deposits, and those in the Moira Sound unit include the Barrier Islands, Moira Copper, Niblack, and Nichols Bay deposits. Pb-isotopic signatures were determined on sulfide minerals (galena, pyrite, chalcopyrite, pyrrhotite, and sphalerite) to constrain metal sources of the massive sulfides and for comparison with data for other deposits in the region. Except for the Ruby Tuesday deposit, galena is relatively rare in most of these deposits. Pb-isotopic signatures distinguish the mainly Cu+Zn&plusmn;Ag&plusmn;Au massive sulfide deposits in the Wales Group from the Zn+Cu&plusmn;Ag&plusmn;Au massive sulfide deposits in the Moira Sound unit. Among the older group of deposits, the Khayyam deposit has the widest variation in Pb-isotopic ratios ( 206 Pb/ 204 Pb=17.169&ndash;18.021, 207 Pb/ 204 Pb=15.341&ndash;15.499, 208 Pb/ 204 Pb=36.546&ndash;37.817); data for the other massive sulfide deposits in the Wales Group overlap the isotopic variations in the Khayyam deposit. Pb-isotopic ratios for both groups of deposits are lower than those on the average crustal Pbevolution curve (&micro;=9.74), attesting to a large mantle influence in the Pb source. All the deposits show no evidence for Pb evolution primarily in the upper or lower continental crust. Samples from the younger group of deposits have scattered Pb-isotopic compositions and plot as a broad band on uranogenic and thorogenic Pb diagrams. Data for these deposits overlap the trend for massive sulfide deposits in the Wales Group but extend to significantly more radiogenic Pb-isotopic values. Pb-isotopic ratios of samples from the massive sulfide deposits in the Moira Sound unit plot on a different trend ( 206 Pb/ 204 Pb=17.375&ndash;19.418, 207 Pb/ 204 Pb=15.361&ndash;15.519, 208 Pb/ 204 Pb=36.856&ndash;37.241) from the steep slope defined by the massive sulfide deposits in the Wales Group. In comparison, the Pb-isotopic ratios of Devonian polymetallic (Pb-Zn-Au-Ag) quartz-sulfide veins vary widely ( 206 Pb/ 204 Pb=18.339&ndash;18.946, 207 Pb/ 204 Pb=15.447&ndash;15.561, 208 Pb/ 204 Pb=37.358&ndash;38.354), straddling the slope defined by the massive sulfide deposits in the Moira Sound unit. The general decrease in 207 Pb/ 204 Pb ratio in these deposits, relative to the average crustal Pb-evolution curve, suggests that the most likely lead sources were those associated with oceanic volcanic rocks. The massive sulfide deposits in the Wales Group may have resided within an intraoceanic tectonic setting where the mantle was the predominant contributor of metals. Some contribution from reworked arc material or recycled older, hydrothermally altered oceanic crust (including pelagic sediment) is also possible. Lead sources of the massive sulfide deposits in the Moira Sound unit also included an older source region, possibly a Late Proterozoic or Cambrian volcanosedimentary sequence and the massive sulfide deposits in the Wales Group. Preliminary regional comparison of the Pb-isotopic data indicates that the Greens Creek (Admiralty Island, Alaska) and Windy Craggy (northern British Columbia) deposits probably did not share a common lead source with the VMS deposits on Prince of Wales Island. Other sulfide occurrences on Admiralty Island are also more radiogenic than those on Prince of Wales Island. Large differences in 207 Pb/ 204 Pb ratio suggest that the lead in the VMS deposits in different parts of the Alexander terrane evolved from sources with heterogeneous U/Pb ratios, resulting from mixing of mantle and crustal components.

Alaska↗
USGS2004

Paleozoic sedimentary rocks in the Red Dog Zn-Pb-Ag district and vicinity, western Brooks Range, Alaska: provenance, deposition, and metallogenic significance

Geochemical analyses of Paleozoic sedimentary rocks in the western Brooks Range reveal a complex evolutionary history for strata surrounding the large Zn-Pb-Ag deposits of the Red Dog district. Data for major elements, trace elements, and rare earth elements (REE) were obtained on 220 samples of unaltered and unmineralized siliciclastic rocks from the Upper Devonian-Lower Mississippian Endicott Group (Hunt Fork Shale, Noatak Sandstone, Kanayut Conglomerate, Kayak Shale), the overlying Carboniferous Lisburne Group (Kuna Formation, unnamed drowned shelf facies), and the Pennsylvanian-Permian Siksikpuk Formation. Major base metal sulfide deposits of the region are present only in the Kuna Formation, which in the Red Dog district comprises siliceous black shale and black chert, minor limestone (calcareous radiolarite), and sparse lithic turbidite and bedded siliceous rock. Gray and rare black shales of the Kayak Shale and common black shales of the Kuna Formation are anomalously low in iron (avg Fe/Ti = 6.25 and 6.34, respectively) relative to other Paleozoic shales in the region (9.58-10.6) and to average shales worldwide (10.1-10.5). In contrast, the bedded siliceous rocks contain appreciable hematite (avg Fe/Ti = 35.0) and high U/Ti and REE/Ti ratios that are interpreted to reflect low amounts of detrital material and a major Fe-rich eolian component. Geochemical data (e.g., MnO <0.01 wt %; avg Cr = 317 ppm), sizes of framboidal pyrite grains, and limited bioturbation suggest anoxic and denitrifying depositional conditions for most black shales of the Kuna Formation; low Mo/Ti ratios argue against euxinic (sulfate-reducing) conditions. Organic-rich black shales of the Kuna Formation with up to 8.4 wt percent C organic and gray to black shales of the Kayak Shale with up to 4.1 wt percent C organic typically have only sparse pyrite (<1 wt % S) and very low iron-limited S/C ratios (mostly <0.2). Immobile element plots (e.g., Th-Zr/10-Sc) suggest that source terranes for all of the formations were dominated by one or more felsic-rich continental arcs; a small proportion of recycled sediments is present locally. A minor mafic igneous component also occurs in several shales of the Kuna and Siksikpuk Formations. High average values for the chemical index of alteration [Al 2 O 3 /(Al 2 O 3 + CaO + Na 2 O + K 2 O)] &infin; 100 for shales of the Endicott Group (76.4-81.5) imply moderate to intense chemical weathering in source areas of these sediments. A lower average for black shales of the Kuna Formation (73.7) does not require such weathering. Textural and geochemical data record the effects of diagenetic and/or hydrothermal fluid flow in some of the Paleozoic rocks. Mobility of P, F, U, and light REE is documented in black shales of the Kuna Formation by phosphate replacements of carbonate clasts and of matrix material surrounding the clasts. A relatively low average Ce/Ce* value of 0.73 for P-poor black shales of the Kuna Formation ( < 0.05 wt % P 2 O 5 ) and a similar Ce/Ce* value of 0.78 for a siderite concretion in Kayak Shale suggest that these diagenetic fluids were oxidizing. Many shales of the Kuna Formation have high (K 2 O &infin; 100)/(K 2 O + Al 2 O 3 ) ratios of 21.0 to 23.0, which contrast with low ratios of generally <18.0 for shales of the underlying Endicott Group. The high ratios in shales of the Kuna Formation reflect preferential reaction of smectite to illite during the Jurassic-Cretaceous Brookian orogeny, owing to high silica activities in pore fluids that were generated by the dissolution of abundant biogenic silica. The distribution and composition of Paleozoic strata in the western Brooks Range may have played a fundamental role in Zn-Pb mineralization of the Red Dog district. In our model, deposition and early lithification of biogenic chert and bedded siliceous rocks in the upper part of the Kuna Formation served as a regional hydrologic seal, acting as a cap rock to heat and hydrothermal fluids during Late Mississippian base-metal mineralization. Equally important was the iron-poor composition of black shales of the Kuna Formation (i.e., low Fe/Ti ratios), which limited synsedimentary pyrite formation in precursor sediments, resulting in significant H 2 S production in pore waters through the interaction of aqueous sulfate with abundant organic matter. This H 2 S may have been critical to the subsurface deposition of the huge quantities of Zn and Pb in the district. On the basis of this model, we propose that low Fe/Ti and S/C ratios in black shale sequences are potential basin-scale exploration guides for giant sediment-hosted, stratiform Zn-Pb-Ag deposits.

Alaska↗
USGS2003

Bedded jaspers of the Ordovician Løkken ophiolite, Norway: seafloor deposition and diagenetic maturation of hydrothermal plume-derived silica-iron gels

Sedimentary beds of jasper (red hematitic chert) in the Ordovician L&oslash;kken ophiolite of Norway are closely associated with volcanogenic massive sulphide (VMS) deposits. The jaspers occur in the immediate hangingwall and laterally peripheral to the large L&oslash;kken (25&ndash;30 Mt) and small H&oslash;ydal (0.1 Mt) VMS deposits, and are exposed discontinuously for several kilometres along strike. Massive or laminated types predominate; jasper-sulphide debris-flow deposits are also abundant near VMS deposits. The jaspers contain hematite-rich laminae showing soft-sediment deformation structures and microtextural evidence that record the presence of a colloidal precursor and an origin as gels. Early textures include: (1) straight or curved chains of hematitic filaments 3&ndash;10 &micro;m in diameter and 20&ndash;100 &micro;m long; (2) branching networks of 15&ndash;25 &micro;m-thick, tubular structures surrounded by cryptocrystalline hematite and filled with quartz and euhedral hematite; (3) small (up to 10 &micro;m) spherules composed of cryptocrystalline hematite and silica; and (4) up to 50 &micro;m silica spherules with hematitic cores. The small filaments seem to have been deposited in varying proportions in the primary laminae, possibly together with hematitic and siliceous microspheroids. Diagenetic changes are represented by polygonal syneresis cracks, and the presence of cryptocrystalline (originally opaline) silica, chalcedony, quartz, carbonate and cryptocrystalline hematite and/or goethite forming botryoidal masses and spheroids <10 &micro;m to 5 mm in diameter. Coarser euhedral grains of quartz, carbonate, and hematite are integral parts of these textures. Bleached, silica-rich jaspers preserve only small relics of fine-grained hematite-rich domains, and locally contain sparse pockets composed of coarse euhedral hematite&plusmn;epidote. The jaspers are interpreted to record colloidal fallout from one or more hydrothermal plumes, followed by maturation (ageing) of an Si-Fe-oxyhydroxide gel, on and beneath the Ordovician sea floor. Small hematitic filaments in the jaspers reflect bacteria-catalysed oxidation of Fe 2+ within the plume. The larger tubular filaments resulted from either microbial activity or inorganic self-organized mineral growth of Fe-oxyhydroxide within the Si-Fe-oxyhydroxide gel after deposition on the sea floor, prior to more advanced maturation of the gel as represented by the spheroidal and botryoidal silica-hematite textures. Bleaching and hematite&plusmn;epidote growth are interpreted to reflect heat and fluids generated during deposition of basaltic sheet flows on top of the gels.

Mineralium Deposita↗
USGS2001

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

This paper presents 25 new 40Ar/39Ar dates from the main calc-alkaline ash-flow sheets and related younger plutons of the western San Juan volcanic field, the ash-flow sheets of the Lake City caldera cycle, and veins and other altered rocks in the Lake City region. The goal of the study was to produce similar quality 40Ar/39Ar ages to those currently published for the eastern and central San Juan Mountains. These new data provide a much more precise chronological framework for interpreting durations of events and their relationship to mineralization than do previously published conventional K-Ar dates for the western San Juan Mountains.

Professional Paper↗
USGS2000

Sm-Nd dating of the giant Sullivan Pb-Zn-Ag deposit, British Columbia

We report here Sm and Nd isotope data for hydrothermal tourmalinites and sulfide ores from the giant Sullivan Pb-Zn-Ag deposit, which occurs in the lower part of the Mesoproterozoic Purcell (Belt) Supergroup. Whole-rock samples of quartz-tourmaline tourmalinite from the footwall alteration pipe yield a Sm-Nd isochron age of 1470 ± 59 Ma, recording synsedimentary B metasomatism of clastic sediments during early evolution of the Sullivan hydrothermal system. Data for variably altered (chloritized and/or albitized) tourmalinites from the hanging wall of the deposit, which are believed to have formed originally ca. 1470 Ma, define a younger 1076 ± 77 Ma isochron because of resetting of Sm and Nd isotopes during Grenvillian metamorphism. HCl leachates of bedded Pb-Zn ore yield a Sm-Nd isochron age of 1451 ± 46 Ma, which is consistent with syngenetic-exhalative mineralization ca. 1470 Ma; this age could also reflect a slightly younger, epigenetic hydrothermal event. Results obtained for the Sullivan deposit indicate that the Sm-Nd geochronometer has the potential to directly date mineralization and alteration in stratabound sulfide deposits that are not amenable to dating by other isotope methods.

British Columbia↗
USGS1979

Mineral resources of the Citico Creek Wilderness Study Area, Monroe County, Tennessee

The proposed Citico Creek Wilderness comprises about 5,670 hectares (56.7 km2) in the Cherokee National Forest south of the Little Tennessee River in easternmost Monroe County, Tennessee. Principal drainages are Citico Creek and Doublecamp Creek. Rocks of the study area include greenschist-facies arkosic metasandstone, metagraywacke, slate, and metaconglomerate of the Great Smoky Group of late Precambrian age. Minor deposits of unconsolidated Quaternary alluvium locally mantle the bedrock. Deformation is shown by asymmetric and overturned folds and by several major faults. More than 500 sample s of soil, rock, and stream sediment were collected and analyzed for 31 major, minor, and trace elements by semiquantitative spectrographic, atomic absorption, and fire assay methods No significant metal anomalies were detected. Concentrations of Cu, Co, As, Pb, and Zn slightly higher than background are found within sulfidic parts of a distinctive stratigraphic unit composed of graphitic slate and metagraywacke. Pyrite and pyrrhotite are the chief sulfide minerals, with traces o f accessory sphalerite, chalcopyrite, galena, and arsenopyrite occurring as microscopic intergrowths. A reconnaissance ground radiometric survey and subsequent neutron activation analyses of selected radioactive rock samples show that the sulfidic parts of the graphitic slate unit have a relatively high content of Th and U, but are not potentially economic. No metallic mineral resources appear to exist within the Citico Creek Wilderness Study Area. Resources of slate, silica, and stone are present, but they display no special qualities to differentiate them from other such material throughout the region. Ceramic evaluation tests on selected samples of slate indicate that the slate would have only marginal use for structural clay products such as brick and tile. Minor sand and gravel deposits occur along a few streams but are present in larger quantities and are more easily recovered in other areas.

Tennessee↗