Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

LODE DEPOSITS – The distribution of small- to medium-sized, historic mines and
numerous small prospects are shown on the geologic map (plate 1). A total of 44 mine
adits, 12 mine shafts, 14 cat cuts/trenches, and about 100 prospect pits were located
during this study (appendix 1). The distribution of these mines and prospects indicates the
most likely areas of potential exploration and development in the Maysville quadrangle.
Most of the significant mines and potential areas for mineral exploration are located in
the Proterozoic terrane in the southwest quadrant of the quadrangle. In addition, three
areas have small- to medium-sized historic mines in the northwest quadrant of the
quadrangle.
The majority of mineralization in the Maysville quadrangle consists of base
metals and precious metals associated with calc-silicate zones (Xcs) in sequences of
amphibolite and hornblende gneiss (Xag and Xhig). On the basis of limited studies of
deposits in the Maysville quadrangle and similar deposits in the region, the deposits have
been previously interpreted as Proterozoic skarn deposits (Heinrich, 1981) or
metamorphosed Proterozoic massive-sulfide deposits (Knight, 1981; Sheridan and
Raymond, 1984; Alers and Shallow, 1996; and Heimann and others, 2005). Since most of
the deposits exhibit features that are associated with both of these deposits types, the
distinction between them is not clear cut and classification of the deposits is
controversial. The interpretation of the deposit types is further complicated by the
common association of younger Proterozoic intrusions, specifically abundant pegmatites
related to the Berthoud Plutonic Suite, and locally Tertiary andesite dikes (Ta) and
epithermal-style veins with the mineralization.
Twelve samples of representative mineralization from mine waste dumps were
selected for commercial multi-element geochemical analyses (table 8; UTM coordinates
for samples are given in appendix 1). Some of the samples are composites from groups
and clusters of mines and prospects. The geochemistry shows the overall copper-leadzinc-silver
character of the mineralization hosted in the Proterozoic rocks in the
Maysville quadrangle. Some samples have anomalous to sub-ore grade gold and
anomalous bismuth. Also of note are the very low values (below detection) of arsenic and
antimony.
Two principal mining areas are present in the northwest part of the Maysville
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