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Howards Pass
Northwest Territories, Canada
Main commodities: Zn Pb Ag

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Howards Pass is an extensive, sub-economic, stratabound zinc-lead deposit on the eastern margin of the Selwyn Basin in north-western Canada, some 200 km east of Faro in the NW Territories.

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The local geology in the Howards Pass area is dominated by the Road River Group, a starved sequence of Middle Ordovician to Early Silurian dark grey- to light grey- weathering black and highly carbonaceous shale and chert, overlain by Middle to Late Silurian orange weathering bioturbated mudstone. The Road River Group overlies the impure basinal carbonates of the Rabbitkettle Formation and overlain in turn by the Devonian to Lower Carboniferous (Mississippian) Earn Group black shale and chert, and clastic units of that hosts the Tom and Jason deposits at MacMillan Pass.

The Howards Pass deposits occur within the lower sections of the Road River Formation, which locally comprises five distinct units as follows:
• A transitional unit separates the basal pyritic shales of the Road River Group from limestone of the underlying Rabbitkettle Formation. The pyritic shales of the Road River Group are up to 30 m thick and are dark grey to black shale and dark grey platy limestone which are typically finely laminated;
• An up to 60 m of massive to weakly laminated to platy, dark grey, weakly pyritic, calcareous dolomitic shale with abundant slump breccias;
• An up to 50 m thick, highly carbonaceous, black cherty, shale and chert, which is an organic carbon-rich unit that forms the stratigraphic footwall to the Howards Pass deposits, and is characterized by delicately laminated framboidal pyrite and abundant graptolites
• The bedded sulphides at Howards Pass are overlain by an up to 50 m thick distinctive black phosphatic chert near the centre of the Howards Pass basin, which is thinly bedded or delicately interlaminated with black carbonaceous chert. This unit extends for over 10 km from the Howards Pass deposit, although the thickness and phosphate content decreases away from mineralisation. Near the Howards Pass deposits, the phosphatic chert contains both concentrically and radially zoned carbonate concretions up to one metre in diameter which are commonly rimmed by pyrite, that weathers to a rusty brown color at the surface.
• An orange-weathering, bioturbated, wispy laminated mudstone of Middle to Late Silurian age. This mudstone can be readily recognized in the field and represents a valuable marker unit for separating black shales of the Road River Group from those of the Earn Group.
• Middle to Upper Devonian rusty weathering calcareous dark grey shale and limestone, dark siliceous shale, baritic mudstone and siltstone, and coarse grained clastic rocks of the Earn Group.

Mineralisation within the Road River Formation occurs as rhythmically laminated, saucer shaped bodies distributed along a 130 km long linear belt coinciding with the interpreted basal basinal facies which parallels the hingeline that defines the edge of the Mackenzie Carbonate Platform to the west which was deposited over the Canadian Shield.

There are two larger deposits at Howards Pass, XY and Anniv, and three smaller accumulations, OP, Hug and Pab. which occur within the NW-SE elongated 35 km long second order basin known as the "Zinc Corridor".   The XY, Anniv and OP deposits occur in local third-order basins within the "zinc corridor".   All are deposited in the Howard's Pass Member of the Road River Formation.   Individual cycles in the unit that hosts the ore exhibit an ascending trend from limestone, through carbonaceous mudstone, to cherty mudstone, to chert.

Sulphide mineralogy consists of fine grained sphalerite, lesser galena and minor pyrite.  The mineralisation is only weakly zoned, has a high degree of sedimentary intercalation, and has negligible silver, and low barium (typically <2000 ppm) and copper contents.

The resource at the deposit has been quoted at >486 Mt @ 5.0% Zn, 2.0% Pb, 9 g/t Ag.

The most recent source geological information used to prepare this decription was dated: 2001.    
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.

    Selected References
Ainsworth B  1991 - Howards Pass lead-zinc deposits: in Hollister V F (Ed.),  Case Histories of Mineral Discoveries, Porphyry Copper, Molybdenum and Gold Deposits, Volcanogenic Deposits (Massive Sulfides) and Deposits in Layered Rock Society for Mining, Metallurgy and Exploration Inc., Littleton, Colorado   v3 pp 141-146
Carne R C, Cathro R J  1982 - Sedimentary exhalative (sedex) zinc-lead-silver deposits, northern Canadian Cordillera: in    CIM Bull   v75, no. 840 pp 99-113
Gadd, M.G., Layton-Matthews, D., Peter, J.M. and Paradis, S.J.,  2016 - The world-class Howard’s Pass SEDEX Zn-Pb district, Selwyn Basin, Yukon. Part I: trace element compositions of pyrite record input of hydrothermal, diagenetic, and metamorphic fluids to mineralization: in    Mineralium Deposita   v.51 pp. 319-342
Gadd, M.G., Layton-Matthews, D., Peter, J.M., Paradis, S. and Jonasson, I.R.,  2017 - The world-class Howard’s Pass SEDEX Zn-Pb district, Selwyn Basin, Yukon. Part II: the roles of thermochemical and bacterial sulfate reduction in metal fixation: in    Mineralium Deposita   v.52, pp. 405-419.
Goodfellow W D, Jonasson I R  1986 - Environment of formation of the Howards Pass (XY) Zn-Pb deposits, Selwyn Basin, Yukon: in Morin J A (Ed.),   Mineral Deposits of Northern Cordillera The Canadian Institute of Mining & Metallurgy   Special Volume 37 pp 19-50
Huston, D.L., Champion, D.C., Czarnota, K., Duan, J., Hutchens, M., Paradis, S., Hoggard, M., Ware, B., Gibson, G.M. Doublier, M.P., Kelley, K., McCafferty, A., Hayward, N., Richards, F., Tessalina, S. and Carr, G.,  2023 - Zinc on the edge - isotopic and geophysical evidence that cratonic edges control world-class shale-hosted zinc-lead deposits: in    Mineralium Deposita   v.58, pp. 707-729.
Jonasson I R, Goodfellow W D  1986 - Sedimentary and diagenetic textures, and deformation structures within the sulphide zone of the Howards Pass (XY) Zn-Pb deposits, Yukon and Northwest Territories: in Morin J A (Ed.),  Mineral Deposits of Northern Cordillera The Canadian Institute of Mining & Metallurgy   Special Volume 37 pp 51-70
Kelley, K.D., Selby, D., Falck, H. and Slack, J.F.,  2017 - Re-Os systematics and age of pyrite associated with stratiform Zn-Pb mineralization in the Howards Pass district, Yukon and Northwest Territories, Canada: in    Mineralium Deposita   v.52, pp. 317-335.
Leach D L, Bradley D C, Huston D, Pisarevsky S A, Taylor R D and Gardoll S J,  2010 - Sediment-Hosted Lead-Zinc Deposits in Earth History : in    Econ. Geol.   v.105 pp. 593-625
Martel, E.,  2017 - The Importance of Structural Mapping in Ore Deposits—A New Perspective on the Howard’s Pass Zn-Pb District, Northwest Territories, Canada : in    Econ. Geol.   v.112, pp. 1285-1304.
McClay K R,  1991 - Deformation of stratiform Zn-Pb(-barite) deposits in the northern Canadian Cordillera : in    Ore Geology Reviews   v6 pp 435-462
Ootes, L., Gleeson, S.A., Turner, E., Rasmussen, K., Gordey, S., Falck, H., Martel., E. and Pierce, K.,  2013 - Metallogenic Evolution of the Mackenzie and Eastern Selwyn Mountains of Canadas Northern Cordillera, Northwest Territories: A Compilation and Review: in    Geoscience Canada,   v.40, pp. 40-69, http://dx.doi.org/10.12789/geocanj.2013.40.005.
Slack, J.F., Falck, H., Kelley, K.D. and Xue, G.G.,  2017 - Geochemistry of host rocks in the Howards Pass district, Yukon-Northwest Territories, Canada: implications for sedimentary environments of Zn-Pb and phosphate mineralization: in    Mineralium Deposita   v.52, pp. 565-593.

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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