Metals and Energy Finance:Advanced Textbook on the Evaluation of Mineral and Energy Projects by Dennis L Buchanan

Author:Dennis L Buchanan [Buchanan, Dennis L]
Language: eng
Format: epub
Publisher: Imperial College Press
Published: 2015-11-26T23:00:00+00:00

5.8 Sedimentary-hosted (SEDEX and Carbonate) Pb, Zn, Ba

Sedimentary-hosted Pb/Zn deposits are associated with sedimentary exhalative Pb–Zn (SEDEX) and carbonated-hosted deposits. The latter were first described in the scientific literature as Mississippi Valley-type but the style of mineralisation is also present in the Irish-type deposits. Mineralisation mainly occurred sub-seafloor by replacement of carbonates during diagenesis. The source of the mineralising fluids is considered to be evaporated seawater and the main depositional mechanism is considered to be the mixing of metalliferous ore fluid with low-temperature bacteriogenic H2S-rich brines.

The term stratiform Zn–Pb–Ba SEDEX deposits was originally introduced as a genetic term and refers to the ore-forming process that is found in local basins or depressions on the seafloor. Examples are: Sullivan and Howard’s Pass (Canada); HYC or McArthur River and Mt Isa (Australia); and Red Dog (Alaska, USA). They contain more than 50% of the world’s reserves of Pb and Zn and more than 25% of global production. The dominant sulphides are galena, sphalerite, pyrite and barite, with lesser amounts of chalcopy-rite. Silver can be present in minor amounts (mostly in arsenic and antimony sulphosalts or in galena). Ore minerals commonly occur in finely-layered horizons, parallel to bedding, interbanded with clastic material and iron sulphides.

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