Search

Discussion of a paper on this deposit, Ontonagon County, Michigan, by W. S. White and J. C. Wright (Econ. Geology, 1954, v. 49, p. 675-716). Four general theories of origin may satisfy the observed geological conditions: 1) the Cu was deposited with the original mud; 2) the Cu, diffusing downward into the uppermost few inches of mud, replaced some primary constituent; 3) the Cu was introduced into the shales from below, prior to final compaction or deformation; 4) the Cu was introduced into the rock after lithification and deformation. The fourth theory is rejected on several counts. The third is favored. The theory of a pretectonic origin for Cu finds support in the distribution and disposition of Cu in shale and sandstone and in the fact that fractures show little relation to shale-ore zones. The typical rhyolites of the region appear to be older than the Nonesuch shale.

The cotangent ruler is a device for measuring directly the dip of contoured surfaces, or, conversely, for constructing contours that represent planes of known dip. It greatly simplifies the graphic solution of problems in structural geology, and has several specialized applications to problems commonly encountered in mining geology and areal geologic mapping.

The source of rhyolitic debris composing conglomerate beds in the Keweenawan lava series of northern Michigan has not been firmly established heretofore. Statistical measurement of imbrication in one bed, the Houghton conglomerate, indicates that the depositing stream flowed from southeast to northwest. The average inclination of pebbles, corrected for the present dip of the bed, is 8 degrees SE. This is compared with the inclinations of imbricated pebbles measured by Krumbein in California flood gravels. In addition, many pebbles in the Houghton conglomerate are inclined at about 40 degrees to bedding it is suggested that these pebbles may have slumped into small scour craters.

http://archive.org/details/determinationofh109459480 U.S. Navy (U.S.N.) authors.

Copper, largely in the mineral chalcocite, is found in the lowermost beds of the Nonesuch shale over many square miles near White Pine, Ontonagon County, Mich. The Nonesuch shale, of late Keweenawan age, is about 600 feet thick and is composed largely of gray siltstone. It overlies 2,300 to 5,500 feet of red sandstones and conglomerates, the Copper Harbor conglomerate. This formation, in turn, overlies the middle Keweenawan Portage Lake lava series, in which occur the famous native-copper deposits of the south shore of Lake Superior. The White Pine mine is 45 to 70 miles west-southwest of the principal native copper mines.The copper-bearing beds at White Pine are primarily in the lower 20to 25 feet of the Nonesuch shale. This cupriferous zone is divided in local usage into four stratigraphic units, which are, in ascending order, the lower sandstone (the uppermost bed of the Copper Harbor conglomerate), the parting shale, the upper sandstone, and the upper shale. The sequence of beds is almost identical in the upper and parting shales, suggesting cyclic sedimentation. This sequence and the distribution of sedimentary facies are attributed to two submergences, separated by an emergence, of a deltaic area.Practically all the copper occurs in the upper and parting shales, except in a small area near the White Pine fault where it is abundant in the upper and lower sandstones. It is present in five different layers in amounts that average from 1 to 3 percent. The total amount of copper in each bed is generally higher where the bed is thick, and thickness, in turn, seems to be greatest in areas that were hollows away from the main channel or channels of the ancient delta. Copper content of the shale beds typically decreases as their sand content increases. The extent of individual copper-bearing beds 1 to 3 feet thick is measurable in square miles.The local occurrence of copper in the upper and lower sandstone beds can be reasonably explained as the result of hydrothermal transportation from the White Pine fault up the dip of the relatively permeable sandstone to the crest of an adjacent anticline. Distribution of copper in the parting and upper shales, on the other hand, seems to be completely independent of local structure, faults, and rock permeability. For the area as a whole the control is lithologic and stratigraphic. Probably the copper was dropped into or precipitated within the original mud; it may conceivably have replaced with exquisite detail something else that was so deposited.

Irradiation of dibenzyl diselenide (l) with 350 nm light in the presence of oxygen afforded benzaldehyde and elemental selenium, whereas irradiation in the absence of oxygen produced dibenzyl monoselenide (ll); irradiation of dibenzyl triselenocarbonate (III) produced dibenzyl diselenide.