Geology of an area about 4 square km covering the outcropping
mineralized zone was mapped at scale 1:2000 on an uncorrected aerial photograph
enlargment. The west part of the zone was mapped at scale 1:500 on a topographic base from
an earlier plane table survey. Andesitic and rhyolitic volcanic and associated
volcanoclastic rocks of probable mid Tertiary age comprise most of the bedrock in the
area. The volcanic rocks disconformably overlie a prevolcanic basement complex of granite,
granite gneiss, and local erosional remnants of marine limestoms and sandstones. Bedrock
exposures are limited to scattered areas along arroyos or to low hills or mine workings.
Poorly consolidated alluvial sand and gravel cover about 80% of the map area. Rock
units mapped are described in the report.
Geochemistry Summary:
Rock chip samples were collected in a rough grid pattern from
both the east and the west zones. The samples were analysized geochemically for Ag, Au,
Cu, Mn, As, and Sb. Analytical results are tabulated in the report. The samples are
grouped in 3 populations as follows: 1) west ore body (samples from within the limits of
the ore zone; 2) east part of west zone (samples from the zone immediately adjoining the
ore zone to the east; and 3) east zone (samples from the extreme eastern part of the
mineralized zone). Results are summarized in the report.
The west ore body is
characterized geochemically by high values of Ag and Cu (the ore zone actually crops out)
and by high Mn. As and Sb are anomalous over a relatively small range. The east half of
the west zone has much lower, but geochemically anomalous silver values, relatively low
manganese and low copper. As and Sb are anomalous and average slightly higher than in the
ore zone, with a greater range of high values. The east zone is characterized by very low
silver, (most less than 1 ppm), and copper values. Scattered anomalies of silver and
copper are present. Manganese values are relatively high. The mode of As and Sb values is
about the same as the west ore body, but a large number of highly anomalous As and
particularly Sb values (i.e. up to 3100 ppm) are present.
The presence of manganese oxides, veins of quartz and barite, and the widespread,
strong anomalies of As and Sb are favorable aspects of the east zone. We interpret the
east zone to be part of the same epithermal system that deposited the west ore body, but
consider the east zone to be higher in the system, and above the silver zone. It is a good
possibility that silver ore bodies similar in size and grade to the west ore body are
present at shallow depths, less than 100 meters in the east zone.
Geophysics Summary:
None Reported
Drilling Summary:
All 25 holes drilled were percussion using a Mission
down-the-hole hammer and a 6.5 inch diameter bit. Phase I drilling was contracted by Pozos
Republicos; Phase II was contracted by Proyectos y Perforaciones Hidraulicas del Noroeste.
An 8 inch diameter collar pipe a minimum of 1 m long was set on each hole. Holes collared
in poorly consolidated alluvium were drilled to bedrodk using a 10 inch diameter rotary
tricone bit. Eight inch diameter PVC pipe was set as casing through the alluvium.
Drill
cuttings were collected after passing through a cyclone. Bedrock samples were collected
over 1 meter intervals for each of the drill holes. The 1 meter samples averaged about 10
kilos.. Each sample was thoroughly mixed, then split. One quarter of the sample was sent
for assays. The remainder of the sample was retained and stored on the prooerty. Pulps
from assays were retained.
All the drill samples were analyzed by Jacobs Assay Office (Tucson) for Ag and Au (fire
assays) and for Cu and Mn (AA). Sample splits for Phase I drilling were fire assayed for
Ag and Au by Valenzuela Laboratories, (Santa Ana, Sonora). Phase II sample splits were
fire assayed for Ag and Au by Metales Santa Ana, (Santa Ana, Sonora). Check assays on
sample splits and pulps were made by Rochin Assay Labs, (Douglas, Ariz.). Assay results
are tabulated and graphic summaries of the assay results are presented in the report.
Detailed lithologic logs of the drill holes were not prepared because of the small size
of the drill cuttings.
Reserves Summary
Drill indicated ore reserves calculated for the west zone are
976,270 tons of weighted average grade 163 gm Ag/ton. An additional 345,000 tons of likely
average grade 170 gm Ag/ton are considered probable adjoining the drill indicated ore to
the south and southeast. A geologic potential for 1 million tons or more of 170 gm Ag/ton
is thought to exist in the east zone.
Other:
Silver Deposits:
Silver-bearing manganese oxide
deposits at the Burnt Rock property crop out in a narrow discontinuous, northwest trending
band in low hills for a distance of 1500 m. The higher grade silver deposits, as now known
on the property, are at the west end of the zone where most of the drilling and sampling
has been concentrated. Only geologic mapping and widely spaced geochemical sampling have
been carried out to date on the eastern part of the zone. The west and the east parts of
the mineralized zone are described in the report.
