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Lik |
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Alaska, USA |
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Zn Pb Ag
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Super Porphyry Cu and Au
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Lik and Su - Alaska, USA - 22 Mt @ 9% Zn, 3.1% Pb, 48 g/t Ag, enclosing a preliminary reserve of 16.5 Mt @ 10.2% Zn, 3.3% Pb, 52 g/t Ag, within a sequence of Carboniferous limestone, chert and shale in the Noatak district of the Brooks Range of Alaska - some 15 to 20 km WNW of the Red Dog deposits.
The deposit comprises semi-massive lenses of pyrite and marcasite with lesser sphalerite and galena in a 2000x500m zone.
Lik and Su are hosted by black siliceous and carbonaceous shales (with 1.5 to >8% total organic carbon) and black cherts belonging to the Early Carboniferous Lisburne Group. These beds contain a few calcareous sandstones, calcareous shales and micrite. The black shales have ball and pillow soft sediment deformation structures and possible inter-clast rip-ups and worm burrows.
The structure is complex with Upper Carboniferous varicoloured mudstones and shales being found in both the structural hangingwall and footwall of the mineralised beds with disseminated porphyroblasts of barite and higher levels of Ba and Mn than the host unit. The stratigraphic footwall is the Lower Carboniferous Kuna Formation calcareous black shales.
The ore zone is interpreted to represent a series of thrust plates (each < 1000x250x13m) repeated by low angle faults.
The dominant sulphides in the Lik mineralisation are pyrite and marcasite with lesser white and cream sphalerite and minor galena. The ore has laminar, nodular, massive, breccia and complexly recrystallised textures.
Laminar ore predominates, but is the style with the lowest grades (<7% Zn and commonly <5% Zn). It is copmposed of streaks, thin foliations (< 1mm) and bands (<30 cm) of fine grained (< tens of microns) iron sulphide and light coloured sphalerite in a black shaly matrix with course grained veinlets and crystals of galena.
Nodular ore is composed of colloform, framboidal and radiating aggregates of pyrite and lesser marcasite with minor interstitial sphalerite and galena.
Massive pyrite rich ore has a homogenous, dendritic or swirled texture composed of silica with coarser stringers of fine grained galena and sphalerite and contains coalesced and overgrown framboids of pyrite-marcasite.
Breccia ore is un-common and contains angular clasts of un-mineralised black shale and laminated iron sulphide rich mineralisation in a fine grained sphalerite matrix.
The complexly recrystallised ores contain dendrites of sphalerite with overgrowths of pyrite, cruciform galena within sphalerite, galena replacing colloform pyrite and rare medium-brown coarser sphalerite, with occassional tetrahedrite and inclusions of bournonite and boulangerite within galena producing higher Ag grades. 70x100x10m lenses of complex ore surrounded by breccia ore parallels the lithological strike in the centre of the mineralised zone and corresponds to the >10% Zn contour.
The most recent source geological information used to prepare this decription was dated: 1996.
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.
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Selected References:
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Schmidt J M 1997 - Shale-hosted Zn-Pb-Ag and barite deposits of Alaska: in Econ. Geol. Mono. 9 pp 35-65
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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