USGS Science⌕ Search

Geology topics

E. M. MacKevett

Publications and source records attributed to E. M. MacKevett.

13 recordsLinked to original sources
USGS1977

The Alaskan Mineral Resource Assessment Program; background information to accompany folio of geologic and mineral resource maps of the McCarthy Quadrangle, Alaska

The McCarthy 1? by 3? quadrangle, in eastern south-central Alaska, contains potentially significant resources of copper and possibly of a few other commodities. This circular and a companion folio of maps represent results of integrated field and laboratory studies in the disciplines of geology, geophysics, geochemistry, and satellite imagery that are designed to provide a modern mineral resource assessment of the quadrangle. The maps are accompanied by descriptive texts, explanatory material, pertinent references, and by a few auxiliary tables and diagrams. This circular provides background information for the mineral resource assessment and integrates the component maps. It also includes a master list of references (see 'Bibliography') relevant to the geology and mineral deposits of the quadrangle.

Circular↗
USGS1977

The Triassic Chitistone Limestone, Wrangell Mountains, Alaska: stressing detailed descriptions of sabkha facies and other rocks in lower parts of the Chitistone and their relations to Kennecott-type copper deposits

Recent investigations show that sabkha deposits were important in the genesis of Kennecott-type copper ore. Massive chalcocite-rich lodes at Kennecott and nearby deposits formed in the lower 110 meters of the Upper Triassic Chitistone Limestone. The Chitistone and superimposed Upper Triassic and Jurassic sedimentary rocks formed in a marine basin on and surrounded by the Nikolai Greenstone, a thick, extensive, largely subaerial succession of tholeiitic basalt with intrinsically high copper content. Lowermost 110 meters of the Chitistone contains three incomplete upward-shoaling lime mud cyclic sequences that each consist of shallow subtidal limestone grading upward to intertidal stromatolitic fine-grained dolomite. The youngest cycle contains well-developed sabkha features and dolomitic pisolitic and laminate crust caliches and underlies shallow-marine limestone. The ore deposits are related to the youngest supratidal cycle. This carbonate cycle represents a regional sabkha facies that developed between 90-110 meters above the Nikolai Greenstone. This facies, which contained abundant gypsum-anhydrite, was exposed to vadose weathering that leached much gypsum-anhydrite and developed a vuggy zone interbedded with porous dolomitic caliche zones. Subsequent marine deposition capped the porous zone with an impermeable seal. The youngest sabkha horizon served as a permeable conduit for the ore-forming solution and was instrumental in localizing the major Kennecott-type ores.

Open-File Report↗
USGS1974

The Border Ranges Fault in south-central Alaska

The Border Ranges fault, a major fault of southern Alaska, can be traced for more than 1,000 km arcuately eastward from Kodiak Island to the St. Elias Mountains. Throughout its extent, the fault juxtaposes upper Paleozoic and lower Mesozoic rocks on the north against upper Mesozoic and Tertiary rocks. This report describes the Border Ranges fault and its geologic setting along an approximately 245-km-long segment in the McCarthy and Valdez quadrangles. It also summarizes information relevant to other parts of the fault and discusses its significance and tectonic implications. In the McCarthy and Valdez quadrangles the fault strikes between N. 60° W. and west. Its dips change from vertical and steeply northward in its eastern part to between 20° and 60° north throughout most of the Valdez quadrangle and reflect the transition from a high-angle reverse fault to a northward-dipping thrust. The Border Ranges fault is interpreted to mark a plate boundary that developed near the close of the Mesozoic or in the early Tertiary.

Alaska↗