Geology and Ore Genesis of Silver–Barite Mineralization in the ...

Propylitic alteration (chlorite+calcite±epidote) is the most pervasive and readily recognizable form of
alteration in the district. The alteration is widespread and commonly not proximal to barite veins.
Silicification, consisting of fine-grained chalcedony and jasperoid is more closely associated with the
silver-barite mineralization. Payne and Glass (1987) also report hydrothermal alteration of amphibole to
celadonite. Local kaolinization is present in host rocks containing phenocrysts of plagioclase.
Oxidized barite veins are thought to represent the supergene equivalent of the black matrix barite veins.
They are easily recognized by the brick red alteration adjacent to and intimately associated with the
barite. The alteration consists of jasperoid and secondary, fine-grained hematite. Most primary sulfides
have been replaced, with only occasional, heavily corroded, pyrite remaining. Galena has altered to
cerrusite. Magnetite has been replaced by hematite, leaving pseudomorphs of the original magnetite
crystals. Secondary silver minerals, particularly embolite and cerargyrite, are present in some veins but
absent in others. Silver grades for the oxidized veins of Wall Street Canyon are quite high, exceeding 10
oz/ton.
Barstow Formation
Fletcher (1986) studied the silver–barite
mineralization of the Middle Miocene Barstow
Formation. He identified two separate tabular ore
bodies: the Waterloo deposit, north of the Calico
fault, and the Langtry, 2.5 kilometers to the west and
on the south side of the Calico fault. He argued that
the deposits were once part of a single ore body that
was subsequently offset by right slip along the Calico
fault. The Barstow Formation in this area is
composed of lacustrine sandstones, siltstones and
mudstones with minor interbedded volcaniclastic
sandstones. Fletcher reports that barite occurs as
disseminated grains and cementing material within
siltstone (99%) (Fig. 5) and more rarely as veinlets (1%). The veinlets have a random orientation in
contrast to the northwest strike of those in the underlying Pickhandle volcanics.
Alteration consists of bleaching that most commonly manifests itself as K-feldspar replacement of
detrital feldspar grains. Although not termed as such by Fletcher, this alteration appears similar to the
pervasive potassic alteration associated with many epithermal precious metal deposits. The alteration is
correlative with an early stage of barite-quartz mineralization. Intense silicification, most commonly as
colloform bands of jasperoidal chalcedony with minor recrystallized quartz is also present. For a more
detailed discussion of the deposits see Fletcher (1986).
Waterman Hills
Figure 5. Photomicrograph of disseminated barite
(white) in siltstone (from Fletcher, 1986).
Silver ore in the Waterman Hills occurs in two northwest-striking veins that can be traced for a distance
of over 500 meters along strike (Ireland, 1993). The veins lie within a sequence of volcaniclastic
sedimentary rocks and volcanics of uncertain age. Dibblee (1952) correlated the rocks with the Miocene
Pickhandle Formation. However, the more silicic nature of the volcanics (rhyolites) and the distinct
northwest strike of the sedimentary units suggest that correlation is tentative. The veins, while