Geology and petrochemistry of the Mount Chase massive sulfide prospect, Penobscot County, Maine

Author

Michael V. Scully

Abstract

"The Mount Chase massive sulfide prospect of northern Penobscot County, Maine was discovered in 1979 by Getty Mining Company. The deposit occurs within a sequence of lower paleozoic metavolcanic and metasedimentary rocks. The footwall units consist of rhyolitic flows, quartz-feldspar crystal tuff, and altered tuffaceous volcanic breccias. These rocks lie unconformably upon intensely folded sediments which are tentatively correlated with the Grand Pitch Formation of probable Cambrian age. The footwall volcanoclastic rocks exhibit a narrow zone of intense chloritic alteration immediately below the massive sulfide horizon, and a broader zone of sericitic alteration below that. A zone of stringer mineralization is associated with the footwall alteration beneath the western side of the deposit. The massive sulfide occurs in two adjacent main lenses occurring approximately within the same stratigraphic horizon. On a microscopic scale, the sulfide minerals exhibit metamorphic recrystallization with porphyroblastic and poikilobastic textures common. The Mount Chase hanging wall units consist of a sequence of relatively unaltered crystal-lithic tuffs, greenstone, and shale. The entire Mount Chase footwall and hanging wall sequence is tentatively correlated with the early to middle Ordovician Shin Brook Formation.

Representative drill core samples were analyzed by x-ray fluorescence for SiO₂, Al2O₃, Fe₂O₃, MgO, Na₂O, K₂O, TiO₂, P₂O₅, MnO, FeS₂, Ba, Cu, Zn, Rb, and Sr. The chemical systems of Bastin and Ossan indicate a combination of metasedimentary and metavolcanic lithologies for the Mount Chase rocks. These results agreed well with mineralogical and textural interpretations. Harker-type variation diagrams indicate depleted levels of CaO, and somewhat elevated levels of Na₂O. K₂O is generally depleted in the hanging wall rocks and elevated in the footwall rocks. These observations are interpreted to be the result of alkali metasomatism in the hanging wall rocks and a combination of alkali metasomatism and hydrothermal alteration in the footwall rocks. TAS and AFM plots of the Mount Chase igneous rocks indicate subalkalic calc-alkaline affinities though the most mafic rocks plot as tholeiites"--Abstract, pages ii-iii.

Advisor(s)

Grant, S. Kerry
Hagni, Richard D.

Committee Member(s)

Watson, John L.

Department(s)

Geosciences and Geological and Petroleum Engineering

Degree Name

M.S. in Geology and Geophysics

Publisher

University of Missouri--Rolla

Publication Date

Spring 1989

Pagination

x, 117 pages, plates (in pocket)

Note about bibliography

Includes bibliographical references (pages 100-105).

Geographic Coverage

Penobscot County, Maine

Rights

© 1989 Michael V. Scully, All rights reserved.

Document Type

Thesis - Open Access

File Type

text

Language

English

Thesis Number

T 5851

Print OCLC #

20191870

Electronic OCLC #

1023811670

Recommended Citation

Scully, Michael V., "Geology and petrochemistry of the Mount Chase massive sulfide prospect, Penobscot County, Maine" (1989). Masters Theses. 733.
https://scholarsmine.mst.edu/masters_theses/733