Zoning in the White Pine copper deposit, Ontonagon County, Michigan

Abstract

The top of the cupriferous zone in the lower Nonesuch Shale of Northern Michigan is characterized by an abrupt zonation of Cu-Fe sulfides which represents a chemical and mineralogic transition into the overlying barren pyritic shale. This narrow fringe forms a blanket-like surface which cross-cuts bedding at shallow angles. Although the ore horizons show strict stratigraphic controls, the actual upper limit of copper mineralization in the White Pine area occurs at various stratigraphic levels 20 to 50 feet above the base of the Nonesuch. A strong inverse correlation exists between the height of the fringe surface in the Nonesuch Shale and the amount of copper in the lowermost shale unit. In local areas along fracture zones, a very minor amount of copper has been channeled upward along some fracture zones producing local anomalous elevations in the fringe surface. The White Pine fault is clearly a post-ore structure which offsets the fringe surface.The ore minerals of the Cu-Fe transition show a step-by-step replacement of ironrich sulfides by paragenetically later copper-rich sulfides. The sequence in ascending order is chalcocite, djurleite, digenite, bornitc, chalcopyrite and pyrite. Abnormal concentrations of Cd and Pb occur immediately above the cupriferous zone. These observations suggest, as others have proposed, that the mineralization of the basal Nonesuch was accomplished by the introduction of copper from the underlying Copper Harbor Conglomerate soon after deposition of the Nonesuch Shale. Copper deposition in the sulfur-rich reducing environment of the Nonesuch occurred in large part by replacement of original pyrite along an upward advancing mineralization front (fringe). Metals more soluble than copper were apparently swept upward before the copper front.Simple mathematical models of infiltration and diffusion processes were designed to test the above hypothesis. Each model results in a mineralization period of about 106 years. It seems entirely possible that these mechanisms could account for the transport of copper into the early unconsolidated Nonesuch sediment. Salt sieving and gravity stratification phenomena may have assisted these basic processes. The ultimate source of copper is open to speculation, but may lie in primary magmatic contributions or extraction of metals from the thick volcanic-sedimentary pile of the Keweenawan basin.

Constraints on Conceptual and Quantitative Modeling of Early Diagenetic Sediment-Hosted Stratiform Copper Mineralization

“…In effect, the Gulf of California is an ideal site for the leaching and transport of copper to form downstream eSSC deposits in modern times. Independent estimates of the time required to form important eSSC deposits tend to call for active circulations of cupriferous brine over millions of years [7,18,27,29]. …”

“…Disseminated copper sulfides were deposited by replacement of disseminated syndiagenetic pyrite [1][2][3][4][5]. Early semi-quantitative modeling followed, both at the deposit-scale [6,7] and basin-scale [8].…”

“…Late stages of sediment-hosted stratiform copper (SSC) mineralization (deposited, for example, during late diagenesis, late veining or orogenic disturbances) are not discussed here. Figure 2, from the 1960s, showed that copper was significantly soluble as chloride complexes (>6 ppm) in low-temperature brines and in the presence of hematite, the prominent pigment of redbeds which commonly underlie eSSCs [6,7]. Although only recognized much later to be misleading, the implication was that the ferric oxide of the redbeds signaled oxidizing conditions and therefore the hematite of footwall redbeds assured that conditions were suitably oxidizing for transporting copper.…”

“…The 200 m-thick Nonesuch graybeds and their basal eSSC-type mineralization are enclosed between a 2 km-thick footwall Copper Harbor Conglomerate and a 4 km-thick hanging wall Freda Sandstone, both presumed to have been basin-wide post-rift erosional products of concurrent rift highlands [22], which should have induced topography-driven flow within the adjacent rift basin aquifers, including the footwall Copper Harbor Conglomerate. Figure 2, from the 1960s, showed that copper was significantly soluble as chloride complexes (>6 ppm) in low-temperature brines and in the presence of hematite, the prominent pigment of redbeds which commonly underlie eSSCs [6,7]. Although only recognized much later to be misleading, the implication was that the ferric oxide of the redbeds signaled oxidizing conditions and therefore the hematite of footwall redbeds assured that conditions were suitably oxidizing for transporting copper.…”

Scientism and Effectiveness in Teaching of Foreign Languages: Content and Language Integrated Learning (Clil)

“…Developing a broad spectrum of positive emotions should go hand in hand with learning tasks and their solutions, results achieved, cooperation between students and a teacher, etc. Brown (1971), Bandura (1977) even mention the necessity of the emotional dimension of a teaching plan. Stuchlíková (2005) presents a detailed elaboration of the problems concerning the relationship between emotion and educational success.…”