The Blackbird cobalt-copper (Co-Cu) district in the Salmon River Mountains of east-central Idaho occupies the central part of the Idaho cobalt belt—a northwest-elongate, 55-km-long belt of Co-Cu occurrences, hosted in grayish siliciclastic metasedimentary strata of the Lemhi subbasin (of the Mesoproterozoic Belt-Purcell Basin). The Blackbird district contains at least eight stratabound ore zones and many discordant lodes, mostly in the upper part of the banded siltite unit of the Apple Creek Formation of Yellow Lake, which generally consists of interbedded siltite and argillite. In the Blackbird mine area, argillite beds in six stratigraphic intervals are altered to biotitite containing over 75 vol% of greenish hydrothermal biotite, which is preferentially mineralized. Past production and currently estimated resources of the Blackbird district total ~17 Mt of ore, averaging 0.74% Co, 1.4% Cu, and 1.0 ppm Au (not including downdip projections of ore zones that are open downward). A compilation of relative-age relationships and isotopic age determinations indicates that most cobalt mineralization occurred in Mesoproterozoic time, whereas most copper mineralization occurred in Cretaceous time. Mesoproterozoic cobaltite mineralization accompanied and followed dynamothermal metamorphism and bimodal plutonism during the Middle Mesoproterozoic East Kootenay orogeny (ca. 1379–1325 Ma), and also accompanied Grenvilleage (Late Mesoproterozoic) thermal metamorphism (ca. 1200–1000 Ma). Stratabound cobaltite-biotite ore zones typically contain cobaltite 1 in a matrix of biotitite ± tourmaline ± minor xenotime (ca. 1370–1320 Ma) ± minor chalcopyrite ± sparse allanite ± sparse microscopic native gold in cobaltite. Such cobaltite-biotite lodes are locally folded into tight F 2 folds with axial-planar S 2 cleavage and schistosity. Discordant replacement-style lodes of cobaltite 2 -biotite ore ± xenotime 2 (ca. 1320–1270 Ma) commonly follow S 2 fractures and fabrics. Discordant quartz-biotite and quartz-tourmaline breccias, and veins contain cobaltite 3 ± xenotime 3 (ca. 1058–990 Ma). Mesoproterozoic cobaltite deposition was followed by: (1) within-plate plutonism (530–485 Ma) and emplacement of mafic dikes (which cut cobaltite lodes but are cut by quartz-Fe-Cu-sulfide veins); (2) garnet-grade metamorphism (ca. 151–93 Ma); (3) Fe-Cu-sulfide mineralization (ca. 110–92 Ma); and (4) minor quartz ± Au-Ag ± Bi mineralization (ca. 92–83 Ma). Cretaceous Fe-Cu-sulfide vein, breccia, and replacement-style deposits contain various combinations of chalcopyrite ± pyrrhotite ± pyrite ± cobaltian arsenopyrite (not cobaltite) ± arsenopyrite ± quartz ± siderite ± monazite (ca. 144–88 Ma but mostly 110–92 Ma) ± xenotime (104–93 Ma). Highly radiogenic Pb (in these sulfides) and Sr (in siderite) indicate that these elements resided in Mesoproterozoic source rocks until they were mobilized after ca. 100 Ma. Fe-Cu-sulfide veins, breccias, and replacement deposits appear relatively undeformed and generally lack metamorphic fabrics. Composite Co-Cu-Au ore contains early cobaltite-biotite lodes, cut by Fe-Cu-sulfide veins and breccias, or overprinted by Fe-Cu-sulfide replacement-style deposits, and locally cut by quartz veinlets ± Au-Ag ± Bi minerals.

Abstract The western Upper Peninsula of Michigan is well known for hosting significant concentrations of copper in copper-dominated deposits. Most of the copper is hosted by rocks of the Mesoproterozoic Midcontinent Rift. Copper deposits in the western Upper Peninsula can be subdivided into two overlapping world-class copper mining districts. The Keweenaw Peninsula native copper district produced 11 billion lbs of copper and a lesser unknown but significant quantity of silver. Native copper deposits in this district are stratiform and hosted by tops of rift-filling subaerial basaltic lava flows and interflow coarse clastic sedimentary rocks. These deposits are interpreted to be the result of mineralizing hydrothermal fluids derived from rift-filling basaltic volcanic rocks that migrated upwards, driven by late Grenvillian compression of the rift some 40–50 million years following cessation of active rifting. The Porcupine Mountains sediment-hosted copper district produced or potentially will produce 5.5 billion lbs of copper and 54 million ounces of silver. These stratiform/stratabound deposits are hosted in rift-related black to gray shale and siltstone and dominated by chalcocite rather than native copper. Chalcocite is interpreted to be the result of introduction of copper-bearing fluids during diagenesis and lithification of host sediments. At the now-closed White Pine Mine, the chalcocite mineralizing event was followed by a second stage of native copper deposition that demonstrates a spatial and temporal overlap of these two world-class mining districts. While these two districts have been dormant since 1996, favorable results from recent exploration at Copper-wood suggest a revival of the mining of copper-dominated deposits in the western Upper Peninsula of Michigan.

The low-temperature epigenetic and stratabound Pb-Zn-Cu-Ba-F-Sr–bearing ore deposits enclosed within sedimentary columns historically have been major sources of metals. Exploration companies still find these deposits to be a profitable exploration target due to their simple mineralogy as well as the large tonnage that can present, always considering the mineral districts as a whole. In northeastern México, several nonmagmatic, low-temperature Pb-Zn-F-Ba deposits have been systematically considered as magmatic-related (skarns, high-temperature replacement deposits, epithermal deposits, etc.). Recently, these deposits have been restudied and placed within a scenario of deep fluid circulation of basinal brines through the Mesozoic sedimentary series, enriched in Ba, F, and metals during fluid flow and water-rock interactions. These fluids gave rise to a series of strata-bound epigenetic ore deposits scattered throughout the whole Mesozoic carbonate platform and can be shown to be unrelated to any period of magmatism. There is no intense alteration to the host rocks. Commonly there is a close association with organic matter, either liquid hydrocarbons or bitumen; they have a very simple mineralogy of barite, celestine, fluorite, sphalerite, galena, and have low formation temperatures (90–105 °C) combined with variable salinities. These characteristics make these deposits similar to the Mississippi Valley–type deposits, possibly most similar to the Alpine-Appalachian subtype.