Niblack - Lookout, Trio, Dama, Mammoth, Lindsy
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The Niblack volcanic hosted massive sulphide (VHMS) copper-gold-zinc-silver deposit comprises several polymetallic sulphide bodies, the most significant of which are the Lookout and Trio Zones. The deposit is located in the southern part of Prince of Wales Island in far southeast Alaska, ~50 km SW and 475 km SSE of Ketchikan and Juneau respectively. It lies to the south, west and north of Niblack Anchorage, a small bay off the northern coast of Moira Sound which is a deep inlet on the eastern coast of the island.
A number of other VHMS and lesser polymetallic quartz-sulphide vein deposits and showings have been outlined on Prince of Wales Island. The more significant of these, apart from the Niblack cluster, include Khayyam and Stumble-On 30 to 40 km to the north.
Prince of Wales Island lies within the Neoproterozoic to early Palaeozoic Alexander Terrane which extends for >1000 km, from western British Columbia, through the 'panhandle' of southeastern Alaska, to the western Yukon Territory and eastern Alaska. The Alexander Terrane is interpreted to have evolved on a convergent plate margin from the Neoproterozoic to Early Devonian. It is characterised by arc-type igneous and sedimentary rocks, which were subjected to deformation and metamorphism during the Middle Cambrian to Early Ordovician, and Middle Silurian to early Devonian orogenic events. Subsequently, shallow marine carbonate and clastic rocks, and subordinate mafic to intermediate volcanic rocks, were deposited, during a period of relative tectonic stability (Gehrels and Saleeby, 1987). A further suite of rift-related volcanic and sedimentary rocks were unconformably deposited over the older rocks during the Late Triassic (Gehrels et al., 1986). The Alexander Terrane was accreted to the inboard Cordilleran terranes during the mid-Jurassic to Cretaceous, resulting in renewed deformation and metamorphism (Berg et al., 1972; Coney et al., 1980). The outer Chugach and related Outer Terranes collided with the Alexander Terrane to the west from the Mid to Late Cretaceous onwards, whilst additional dismemberment along regional-scale dextral strike-slip faults continued throughout the Tertiary and into Recent times. See the Rocky Mountain Tectonic Summary for an overview.
Prince of Wales Island and Niblack fall within the Craig Sub-terrane, which makes up much of the southern half of the Alexander Terrane. This terrane also hosts other VHMS deposits of different ages, e.g., the Triassic Greens Creek on Admiralty Island, ~450 km to the NNW, also in the Alaskan 'panhandle', and Windy Craggy a further 330 km to the NW, in far northwestern British Columbia, Canada. Both Greens Creek and Windy Craggy are within the Admiralty Terrane, which occurs in the northern half of the Alexander Terrane and is characterised by continental platform sequences. The Craig subterrane was thrust over the Admiralty subterrane during the Permian. Both of these subterranes are exposed in the Greens Creek-Juneau area, whilst a third, the Elias Subterrane is overthrust onto the previous pair further to the north. Windy Craggy is exposed in a window through the Elias Subterrane (Steeves, 2018).
The Craig Sub-terrane is composed of three stratigraphic units which record episodic growth of oceanic volcanic arcs and arc-proximal basin sedimentation (Berg et al., 1978; Gehrels and Berg, 1994), namely the:
• Wales Group, the oldest rocks on the island, which comprise Neoproterozoic to Cambrian submarine basaltic to rhyolitic lavas and volcaniclastic
rocks, turbidites and limestones. These have been metamorphosed to greenstone and amphibolite, felsic schist and gneiss, graphitic phyllite, minor marble and sparse metaconglomerate. The Wales Group hosts much of the VHMS mineralisation on the island. It's age is constrained by a concordant U-Pb zircon age of 554 ±4 Ma for a crosscutting granitic (now orthogneiss) pluton on southern Dall Island (Gehrels, 1990)
• Moira Sound Unit, that comprise Ordovician to Silurian andesitic volcaniclastic rocks, turbidites, graphitic limestones and cherts that unconformably overlie the Wales Group and host some of the more significant mineralisation (Slack et al., 2005; Karl et al., 2009); and
• Descon Formation, composed of Cambrian to Early Devonian marine sedimentary rocks that conformably overlie the Moira Sound unit, but were intruded by a 465 to 425 Ma diorite, quartz diorite, and tonalite igneous complex.
Plutonic rocks are abundant on Prince of Wales and adjacent islands, and vary widely in age and petrology, including Late Neoproterozoic, Ordovician, Silurian, Devonian, Permian, Jurassic and Cretaceous (Gehrels and Saleeby, 1987; Karlet al., 2005) and compositions ranging from granite, through syenite to gabbro and pyroxenite. The younger of these intrusions are related to the Coast Magmatic-Metamorphic Belt which adjoins the Alexander Terrane to the east.
Two major orogenic events are evident on Prince of Wales and surrounding islands (Slack et al., 2005):
• D1, the Wales Orogeny - A middle Cambrian to earliest Ordovician lower greenschist to upper amphibolite facies metamorphic event that only affects the Wales Group, suggesting D1 predated the deposition of the succeeding two units (Gehrels and Saleeby, 1987; Gehrels, 1990). It is characterised by the development of S1 foliation and regional-scale uplift accompanied by regional- and outcrop-scale isoclinal to recumbent folds.
• D2, the Klakas Orogeny, which represents a widespread Silurian to Early Devonian deformation event that is found throughout the Craig subterrane.
VHMS mineralisation on the island is restricted to the Wales Group and sections of the Moira Sound unit. According to Slack et al. (2005), the largest past producers are the Khayyam and nearby Stumble-On deposits, hosted by the Wales Group, at the head of McKenzie Inlet, which were mined from 1901 to 1907, together producing 0.21 Mt of massive sulphide ore averaging 1.7 wt.% Cu, 9.6 g/t Ag, 1.9 g/t Au (Barrie, 1984; Barrie and Kyle, 1988). Khayyam has an additional estimated remaining resource of 0.0787 Mt of massive sulphide averaging 2.9 wt.% Cu, 0.8 wt.% Zn, 17 g/t Ag, 1.3 g/t Au (Maas et al., 1995). The Copper City Mine produced 77 t Cu, 146 kg Ag, and 10.6 kg Au between 1903 and 1905; the Corbin Mine produced smaller amounts, totalling 9.7 t of Cu and 12 kg of Ag between 1906 and 1913 (Bufvers, 1967). The Niblack deposit was mined on 5 levels to a depth of 90 m between 1902 and1908, and produced 18 000 t of ore averaging 4.9 wt.% Cu, 34 g/t Ag, 2.3 g/t Au (Maas et al., 1995).
The initial discovery of copper was made at Niblack Anchorage in 1899, followed by development of the Niblack Mine on the site of the initial discovery. Between 1974 and 1976, the Niblack area was explored by Cominco American Incorporated. In 1977, The Anaconda Company took over the leases and secured additional ground, to conduct further exploration, locating gold-bearing limonitic mineralisation at surface on Lookout Mountain. In 1980, Noranda Exploration Incorporated optioned the property and conducted a drilling program. In 1984, Lac Minerals (USA) Incorporated entered into a joint venture with Noranda and conducted exploration in two programs until 1993, including further drilling. In early 1995, Abacus Minerals Corp. acquired the rights to the Niblack property from Barrick and Noranda and continued exploration and drilling, culminating in resource estimates at the end of both the 1996 and 1997 field seasons. An 850 m long exploration decline was constructed and an underground exploration program was commenced in 2007. After various deals and name changes, the title holder by 2020 was Blackwolf Copper and Gold Ltd who continue to expand the resource.
By 2021 the known Mineral Resources at the Lookout Zone, were (Black Wolf Copper and Gold Limited press release, 16th June, 2021):
Indicated Resources - 5.64 Mt @ 0.95 wt.% Cu, 1.73 wt.% Zn, 1.75 g/t Au, 29.52 g/t Ag; and
Inferred Resources - 3.4 Mt @ 0.81 wt.% Cu, 1.29 wt.% Zn, 20.1 g/t Ag, 1.32 g/t Au.
According to McNulty et al. (2014) Trio Zone has an:
Inferred Resources - 2.370 Mt @ 1.00% Cu, 1.11 g/t Au, 1.56% Zn, 16.56 g/t Ag;
(although this may be included in the Inferred Resource for the Lookout Zone above which McNulty et al. (2014) quote as having an
Inferred Resources - 1.0203 Mt @ 0.73% Cu, 1.42 g/t Au, 1.17% Zn, 21.63 g/t Ag.
The nearby Dama, Lindsy/88 and Broadgauge prospects also locally contain significant amounts of Zn, Cu, Ag and Au, as described below (Adamson and Gray, 1995; Niblack Mining Corp).
The polymetallic mineral deposits and significant occurrences in southeastern Alaska include:
• Late Neoproterozoic to Cambrian metamorphosed VHMS deposits, hosted in mafic and felsic schist of the Wales Group, which include the Niblack, Khayyam and Stumble-On 'deposits'. The host rocks and massive sulphide deposits underwent two ductile-deformational events and were variably metamorphosed to greenschist to amphibolite grade. The coarse grain size, >1 cm diameter, of the sulphides reflects extensive metamorphic recrystallisation. The massive sulphides of these occurrences are base-metal rich with higher Cu/Zn ratios than those found in the younger Moira Sound Unit (Ayuso et al., 2005).
• Palaeozoic VHMS deposits and occurrences hosted in Ordovician to Early Silurian felsic volcanic rocks of the Moira Sound Unit e.g., on the Barrier Islands, Nichols Bay and elsewhere in Moira Sound. Mineralisation includes gold, silver and base metals, which are generally proportionately richer in Ag relative to base metals and Au. Host rocks are dominantly intermediate to felsic in composition and include volcaniclastic protoliths. Felsic pyroclastic rocks and silicic rhyolite intrusions are interspersed with the mafic volcanic rocks, in addition to volcanic wacke and mudstone turbidites, black carbonaceous limestone, bedded limestone and chert, and argillite containing Early to Late Ordovician graptolites and conodonts (S.M. Karl et al., unpub., quoted by Ayuso et al., 2005). Dacites have been dated at 475 Ma (U-Pb zircon) and basalts contain amphiboles with ages of 484 Ma (Ar-Ar; Wooden, in Karl et al., 2003), while widespread intermediate composition plutons yield ages of 427 to 438 and 465 to 480 m.y. (U-Pb zircon, Gehrels, 1992; Friedman, 2005; Karl et al., unpub., quoted by Ayuso et al., 2005). The Moira Sound Unit and associated massive sulphide mineralisation are less deformed and generally have a lower metamorphic grade of greenschist facies. Two deformation events, the first of which is ductile in the Devonian and the second brittle in the Cretaceous, as well as one episode of folding, have affected the Moira Sound unit (Haeussler et al., 2005).
• Polymetallic Quartz-Sulphide Veins, mainly cutting schist and gneiss of the Wales Group, e.g., the Lady of the Lake, Moonshine, Lucky Boy and Port Bazan. Such veins are rare in post-Ordovician rocks on Prince of Wales and Dall Islands (Herreid et al., 1978). Two generations of quartz veins have been observed in some occurrence (Herreid et al., 1978), with undeformed quartz veins cutting folded predecessors. In contrast to the massive sulphide deposits, these polymetallic quartz-sulphide veins are commonly galena rich. They also contain pyrite, chalcopyrite, sphalerite and, in some places, sparse barite (Herreid et al., 1978; Maas et al., 1995). Dolomite-bearing quartz-sulphide veins are common in rocks of the Wales Group (e.g., Moonshine) but have never been observed in rocks of the Moira Sound Unit (Herreid et al., 1978). At the Dew Drop occurrence, a gold-bearing quartz fissure vein occurs in a fault cutting folded Ordovician metavolcanic and andesitic volcaniclastic greywacke turbidites of the Descon Formation (Churkin and Eberlein, 1977; Karl et al., 2006).
There has been uncertainty over the age of the hosts to the Niblack mineralisation. These hosts comprise a sequence of coherent and volcaniclastic felsic rocks that lithologically resemble the Wales Group, but because of the apparent lack of deformation and metamorphism in comparison to most of that group, have been thought to be part of the Moira Sound Unit of Descon Formation. However, precise crystallisation and maximum depositional ages for six samples of felsic volcanic and intrusive rocks from Niblack by Oliver et al. (2021) has established age constraints for the Niblack felsic succession of i).) crystallisation ages of 565.1 ±0.9 and 564.8 ±1.0 Ma for coherent rhyolite flows; ii).) maximum depositional
ages of 565.3 ±0.9 and 565.2 ±0.9 Ma for felsic volcaniclastic rocks; iii).) a crystallisation age of 565.2 ±0.9 Ma for a quartz-feldspar-phyric subvolcanic sill; and iv).) a crystallisation age of 564.8 ±1.0 Ma for a felsic dyke that crosscuts the Niblack felsic succession. These results indicate the ~200 m thick Niblack felsic succession and VHMS mineralisation formed during a single episode of felsic volcanism at ~565.1 ±0.9 Ma and are thus confirmed as part of the Neoproterozoic Wales Group. Never-the-less, the observation that the host sequence has only undergone low-grade, greenschist facies metamorphism and has apparently only been subjected to one major phase of deformation, is inconsistent with this interpretation.
The stratigraphic sequence in the immediate Niblack area has been deformed into a number of moderate to tight northerly verging folds. Structural observations indicate the main recognised structural event has folded the sequence into a moderately southeasterly plunging antiform, the core of which is occupied by younger mafic volcano-sedimentary rocks. This has been interpreted to indicate that the entire sequence had been overturned during a previously unrecognised deformation that formed large scale, thin-skinned, weakly metamorphosed recumbent fold structures prior to the folding event that produced the principal antiform. As such, the deposit hosts have been subjected to two deformations.
The succession at Niblack Anchorage, consists of a bimodal mafic-felsic suite of volcanic flows and volcaniclastic rocks, overlain by a younger volcano-sedimentary cover with lesser flows. Lithogeochemical data combined with detailed volcanic lithofacies suggest the host succession was deposited in a juvenile oceanic back-arc basin tectonic setting (McNulty et al., 2014). The local stratigraphy can readily be divided into three main units:
• Niblack Stratigraphic Footwall Succession that is primarily composed of dacitic and basaltic volcanic and volcaniclastic rocks, and is at least several hundred metres in thickness. The stratigraphically lowest lithologies comprise argillaceous lithic wackes, overlain by poorly bedded intermediate tuffaceous rocks. These are followed by a thick, monotonous suite of dacitic flows which form the bulk of the Footwall Succession. These volcanic rocks are massive and often moderately pyritic, forming a thick, laterally continuous sequence, with minor intercalations of clastic and volcaniclastic material. The dacitic flow sequence is overlain by amygdaloidal-vesicular mafic flows that frequently exhibit well developed pillow structures. At Lookout Mountain, these mafic flows form the immediate stratigraphic footwall to the Niblack Felsic Succession, although elsewhere they are in structural contact with the felsic volcanic rocks across the Blue Belle Fault.
• The Niblack Felsic Succession, principally felsic flows and volcaniclastic rocks that host all known sulphide occurrences an Niblack. The succession is dominated by mostly rhyolitic, quartz-crystal rich tuffaceous and fragmental volcaniclastic rocks, with lesser aphyric to moderately porphyritic (quartz ±feldspar) rhyolitic flows and domes. The fragment size of the felsic volcaniclastic rocks range from fine lithic (ash) and ash-crystal tuffs through to coarse block-tuff fragmental rocks. Many of these rock types contain variably abundant, coarse, sometimes fractured, often bluish, quartz crystals. The host of the Lookout Zone mineralisation is composed of coarse grained, block-tuff fragmental rocks regarded as representing pyroclastic debris and/or autoclastic talus adjacent to flow-dome complexes. The proximal facies is dominated by coarse rhyolite fragments, with minor rhyodacitic to dacitic components. More distally, these debris accumulations transition to mass flow deposits and debris aprons, and become progressively finer grained and increasingly heterolithic, also containing mafic fragments. These coarse grained, variably polylithic fragmental rocks are an important host to the main mineralisation, with an apparent broad correlation between fragment size, and by inference porosity-permeability, with total sulphide content. Where readily measured, the thickness of the Niblack Felsic Succession is typically ~100 m, with local variations due to folding and faulting, and uneven topography of the seafloor.
Another of the principal component of the sequence are coherent, laterally continuous massive quartz-phyric felsic flows, with hyaloclastite-rich aprons along the flow margins. Proximal to mineralised zones, e.g. Trio, Lookout and Dama, these flows may be cut by well-formed sulphidic stockworks (Oliver, 2010). Other lithologies include two of similar rhyolitic composition, but different appearance. The first is a pale grey-blue, often moderately magnetic, and very fine grained rock, with 5 to 10% sub-mm sized quartz phenocrysts set in an amorphous groundmass. The second is an intrusive, comprising a coarsely porphyritic rock with 15 to 25%, 3 to 5 mm diameter, often bluish quartz (and feldspar) phenocrysts, set in a very fine grained, variably dark, vitreous groundmass. These bodies are typically found at or near the contact between the felsic tuffaceous and overlying mafic volcano-sedimentary assemblage and are post-mineral.
The felsic succession has undergone widespread hydrothermal alteration throughout, mainly manifested as silica-sericite, with or without pyrite, but also chlorite and to a lesser extent epidote that are common in many places, typically being more pronounced in the stratigraphic footwall to the mineralisation. However, as the Niblack assemblage has undergone low-grade greenschist facies regional metamorphism, not all chlorite-epidote alteration is definitely of hydrothermal origin. Variable magnetite is often very strong in the immediate footwall, generally 1.7 to 3 m below the mineralisation.
• Niblack Stratigraphic Hanging Wall Succession, which conformably, and locally gradationally, overlies the felsic succession and caps the hydrothermal system at Niblack. It is principally composed of moderately to strongly magnetic mafic volcano-sedimentary rocks and basaltic flows. The bulk of the volcano-sedimentary succession comprises tuffaceous wackes and finer grained mafic siltstones. The finer grained wackes and siltstones are often thinly laminated with evidence of soft sediment deformation, whilst the coarser grained wackes tend to be massive and thickly bedded. Although much of the volcano-sedimentary sequence is finer grained, and considered to be distal turbidites, coarse grained reworked mafic fragmental units are fairly common in the upper parts of the sequence. Strongly magnetic, pillowed mafic flows, which are a major component, comprise up to 30% of the succession, occurring at several stratigraphic intervals within the mafic volcano-sedimentary assemblages (Oliver 2010). Other minor constituents of the Hanging Wall Succession include beds of coarse reworked felsic fragmental rocks, commonly containing sedimentary rip-up clasts, and sporadic, laminated, magnetic cherty horizons. Mineralisation within the Hanging Wall Succession is limited to thin pyrite laminations within cherty mudstones immediately above the Lookout Zone, with associated minor silicification of mudstones and siltstones above the contact.
• Mafic Dykes which cut all of the units described above and are post-mineral. The most common dyke set is fine grained, aphanitic and often Ca-carbonate altered, ranging in size from 1.5 to 3 m in thickness. Others include fine grained mafic, variably plagioclase-phyric dykes and coarser grained dolerites, relatively coarse grained, coarsely plagioclase-phyric diorite and a final set of basaltic dykes.
The two most important faults in the deposit area are the Blue Belle and the Niblack fault. The Blue Belle fault is an intense, relatively planar, ductile shear zone that localised brittle failure zones. It strikes generally east-west, with dips of 55 to 65°S in the immediate vicinity of the Lookout Zone. This structure has been traced from the top of Lookout Mountain, through the Lookout Zone, east toward the Trio Zone and beyond. Strike-slip displacement is likely not more than a few hundred metres. The Blue Belle fault truncates the sulphide mineralization in the uppermost reaches of the Lookout Zone.
At least six main massive sulphide occurrences are known at Niblick, namely, Lookout, Trio, Dama, Mammoth, Lindsy and the historic Niblack Mine. Only Lookout has been tested sufficiently to estimate Mineral Resources. The Lookout and Trio zones have been subjected to the most detailed investigation. Both are located on the overturned limb of the main antiform that has folded the overturned sequence, and are separated by a strike interval of ~300 m,
Lookout Zone, where sulphide mineralisation has been defined over a strike length of ~250 m and down plunge for ~700 m to a vertical depth of ~ 550 m, with an average thickness of 21 m, but locally up to more than 120 m. The bulk of the higher grade sulphide mineralisation occurs as a number of stacked, sub-parallel, partially interconnecting lenses. These lenses are grade shells, separated by lower grade intervals, and are not usually geological entities. The higher grade lenses appear to reflect zones of greater porosity-permeability within the complexly intercalated coarse fragmental rocks and the finer tuffaceous units. However this relationship is not absolute, as high grade mineralisation sometimes occurs even within compact, fine grained, ash tuffs. The coarse hosts are interpreted to represent intermittent debris flows and coarse talus debris deposited along small scarps formed during active faulting. In the heart of the Lookout Zone, stacked lenses cumulatively comprise 50 to 60 m true thickness of stratigraphy separated by only two or three 3 to 5 m intervals of lower grade mineralisation. Individual lenses vary in down-plunge extent, with the largest lens defined being <300 m long. Increased thicknesses can also occur within hinge zones of parasitic folds on the limbs of the major structure.
The sulphide and precious metal mineralisation is relatively simple, dominated by pyrite, sphalerite and chalcopyrite. The sphalerite is notable for its exceptionally pale colour, typical of low Fe-content sphalerite. Similarly, sulphide grain sizes are typically in the 0.1 to 1.0 mm range. These sulphides occur as massive and net textured semi-massive varieties (i.e., >50% and 25 to 50% sulphide respectively), passing out into disseminated and stringer mineralisation, and have been interpreted to represent sub-sea floor replacement. The semi-massive and massive sulphides contain remnant quartz crystals, ancillary lithic ash and even large volcaniclastic fragments as common gangue components, even within the ‘massive sulphide’ zones. The outer stringer-disseminated zones comprise <25% sulphide, with no sharp distinction between either stringer or disseminated styles based on sulphide content. Where total sulphide decrease to <20 to 25%, both styles are usually present, particularly where there is at least some sphalerite, as this tends to form 'wispy' stringers rather than disseminations. In contrast, pyrite frequently occurs as individual grains or fine micro-aggregates, while chalcopyrite may be found as either irregular granular patches or stringers. A study of 10 high grade samples containing 5.5 to 13.5 g/t Au (Gregory, 2010) found that ~60% of all gold grains were electrum, with the other 40% comprising the mineral petzite, an Au-telluride. Similarly, other than in electrum, Ag was found to be almost exclusively hosted in hessite, an Ag-telluride. The mean size of 250 'gold-bearing' grains was 4.0 µm. Temperature estimates from chlorite microprobe data indicate the sulphide mineralisation of the Lookout Zone, with a 1:1 Cu:Zn and 1:10 Au:Ag composition and chlorite-rich alteration, formed at 321 ±19°C (McNulty et al., 2014).
A gold and silver rich oxide zone is developed in the upper 50 to 60 m below surface of the Lookout Zone, to a maximum of ~100 m. It has a strike length of ~100 m with an average width of ~20 m, splitting at depth to follow the Blue Bell Fault and the steeply dipping sulphide zone. In the oxide interval, base metals have been leached and the rock contains variable goethite and hematite and is typically vuggy. The vugs are interpreted to result from the dissolution of primary sulphide. Locally, zones of iron-oxide cemented, collapse breccias also occur. Secondary copper and zinc oxide mineralisation is generally rare, and it is assumed the bulk of these metals have been leached and flushed out of the immediate area. The zone is cut by the Blue Belle Fault that closely parallels its hanging wall side and likely acted as a permeable conduit for meteoric waters.
Trio Zone, which contains sulphide mineralisation similar to that in the Lookout Zone, to the extent that it occurs in stacked lenses. However at Trio, there are also more massive sulphide zones, interpreted to have been deposited on the sea floor, with associated stringer-style mineralisation. These sulphide accumulations are typically massive and featureless, or locally weakly banded pyritic sulphides, with variable amounts of chalcopyrite and/or pale sphalerite. The mineralised zone has a strike length of ~107 m, persists down dip plunge for ~335 m, with an average thickness of 67 m, made up of a series of narrow lenses that follow the overall felsic stratigraphy, with mineralisation following the margins of an intensely veined, rhyolite flow/dome complex.
Dama Zone, which is located 850 m east of the Trio Zone, located in the hinge of the main antiformal structure detailed above. Massive sulphides have been intersected close to the fold hinge, at the contact between rhyolitic and dacitic rocks of the Felsic and Footwall successions respectively.
Mammoth Zone, where sulphide mineralisation occurs in the unit hosting the Lookout Zone, close to the contact with the overlying Hanging Wall Succession. Mineralisation comprises semi-massive and massive pyrite ±chalcopyrite that has been delineated over a strike length of 160 m and ~150 m down dip.
Lindsy Zone, also known as the Lindsy 88 Showing, which outcrops 700 m east of the Mammoth Zone on the lower, northern slope of Lookout Mountain. It consists of sulphide fragments up to 1.0 m across, with varying composition, set in a quartz-crystal bearing rhyolitic fragmental rock.
Niblack Mine, which was historically mined (see above) to a depth of 90 m below surface, and over a maximum strike length of 80 to 90 m. The deposit has a partial U shape in section, hosted within a synformal core of the Niblack Felsic Succession, the northeastern limb of which is truncated and juxtaposed against the Moira Sound Unit across the SW dipping Niblack Fault, and overlain to the SW by the Stratigraphic Hanging Wall Succession. Mineralisation was mined from lenses dipping at ~60°S, and varying in thickness from 0.5 to 10 m. Drilling has extended the known massive sulphides to 110 m down-dip of the historic workings where the strike length appears to narrow to ~50 m at depth. The Niblack Mine is one of few occurrences in the Niblack area where jasper, with associated massive magnetite, is common, and is found in direct contact with the poorly-banded massive (>90%) sulphide. Zinc was not recovered or reported in the mine's production records, but recent drilling clearly indicates sphalerite is an important component of the massive sulphide.
The information in this summary is drawn from the references listed below and from "Nowak, M., Johnson, M., Rowe, D. and Van Der Heever, D, 2011 - Mineral Resource Estimation, Niblack Polymetallic Sulphide Project, Alaska, U.S.A.; an NI 43-101 report prepared by SRK Consulting, Canada, for Heatherdale Resources Ltd. and Niblack Mineral Development Inc., 140p.
The most recent source geological information used to prepare this summary was dated: 2021.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
Ayuso, R.A., Karl, S.M., Slack, J.F., Haeussler,P.J., Bittenbender, P.E., Wandless, G.A. and Colvin, A.S., 2005 - Oceanic Pb-Isotopic Sources of Proterozoic and Paleozoic Volcanogenic Massive Sulfide Deposits on Prince of Wales Island and Vicinity, Southeastern Alaska: in Studies by the U.S. Geological Survey in Alaska, 2005, U.S. Geological Survey, Professional Paper, 1732-E, 20p.|
McNulty, B., Gregory, M.J., Oliver, J. and Roberts, K., 2014 - Geology and fluid genesis of the Neoproterozoic Niblack Cu-Au-Zn-Ag volcanic hosted massive sulfide camp, southeast Alaska, USA: in Building Exploration Capability for the 21st Century, SEG 2014 Conference, Keystone, CO, USA., Society of Economic Geologists, Conference Abstracts 2p.|
Oliver, J., McNulty, B. and Friedman, R., 2021 - High-precision Ca-Id-Tims age constraints on the Niblack Cu-Zn-Au-Ag deposits: a Neoproterozoic volcanic-hosted massive sulfide deposit in the North American Cordillera: in Econ. Geol. v.116, pp. 1467-1481.|
Slack, J.F., Shanks III, W.C., Karl, S.M., Gemery, P.A., Bittenbender,P.E. and Ridley, W.I., 2005 - Geochemical and Sulfur-Isotopic Signatures of Volcanogenic Massive Sulfide Deposits on Prince of Wales Island and Vicinity, Southeastern Alaska: in Studies by the U.S. Geological Survey in Alaska, 2005, U.S. Geological Survey, Professional Paper, 1732-C, 37p.|
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