I saw the following Hank and realize I don't know the common bottom limits for open pit mines. Do you? 400 ft? or 800ft?
I appreciate that grade, overburden and such and size of orebody dictates, but whats probable ranges?
Thx
C
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American Bonanza encounters gold at Copperstone
American Bonanza Gold Mining Corp BZA
Shares issued 174,801,461 Mar 17 close $0.255
Thu 18 Mar 2004 News Release
Mr. Giulio Bonifacio reports
AMERICAN BONANZA DRILLS HIGH GRADE GOLD IN THE SURFACE DRILLING PROGRAM AT
COPPERSTONE
American Bonanza Gold has released positive drill results from the surface
drilling program at its 100-per-cent-owned Copperstone project in Arizona.
The surface drilling program is designed to conduct exploration and provide
data for resource estimation, with the goal of producing a measured
resource in and around the D-Zone and the C-Zone.
The surface drilling program has begun to the north of the open pit,
southeast of the C-Zone, and approximately 1,000 feet southeast of the
D-Zone, which is currently the subject of a detailed underground drilling
program. The first hole in the surface drilling program encountered a
13-foot (four-metre) interval grading 0.77 ounce of gold per ton (26.5
grams per tonne gold) with 0.5 per cent copper. The following table is a
summary of the assay results for the first drill hole from the surface
drilling program; the hole was drilled on a 180-degree azimuth (due south):
Drill Hole
hole No. length Dip From To
(feet) (deg.) (feet) (feet)
CRD-04-01 885 -82 814.5 827.5
Inter-
Drill val Gold Gold
hole No. length grade grade Copper
(feet) (opt) (g/t) (%)
CRD-04-01 13 0.77 26.5 0.5
The above result is very near the true thickness of the mineralized
structure. CRD-04-01 was drilled with 720 feet of reverse circulation
followed by 165 feet of core drilled at the bottom of the hole. The
mineralized zone was encountered in core portion of the drill hole.
Recoveries from the surface drilling program to date are excellent. While
not drilled on a grid, the nearest drill hole to CRD-04-01 is approximately
140 feet distant with the nearest other drill holes being over 200 feet
distant.
Drilling continues on the surface program to target the Copperstone fault
with two drilling rigs currently working and additional rigs to be on site
soon. CRD-04-01 is the first hole of a 30,000-metre surface drill program
that will continue through most of 2004. Results from additional drill
holes will be reported as they become available. All assays at Copperstone
are at least triple-checked routinely.
Brian Kirwin, president and chief executive officer, stated: "These very
positive results over minable widths are an encouraging indication of the
potential of Copperstone to ultimately support a significant, low-cost gold
mine. It is important to note that this ore-grade intercept was discovered
utilizing our geologic model. This model is constantly under revision as
new information is gathered and serves us well as a predictive tool in our
definition drilling program."
Additional information concerning this drill hole is available on the
company's Web site, www.americanbonanza.com, on the Copperstone page.
Detailed information
The Copperstone gold mineralization occurs within a package of sedimentary
and volcanic rocks, in northwest striking, moderate to shallow dipping
fault zones, principally the Copperstone fault. Intensely sheared, altered
and replaced rock characterizes the Copperstone fault in the vicinity of
the D-Zone. Alteration consisting of intense hematite and magnetite
replacement, chloritization and silicification has been observed in the
Copperstone fault underground and is consistent with alteration visible in
previous drilling.
Gold mineralization is restricted to these fault zones, with little to no
gold mineralization present in the wall rocks. Future exploration and
development efforts will target these mineralized faults to follow up along
strike and dip from the current results and previously drilled
mineralization.
Drilling services are being provided by an international drilling
contractor, Layne Christensen Company of Chandler, Ariz. The drilling and
assaying are conducted under the supervision of Gregory French, CPG No.
10708, a qualified person as defined in Canadian National Instrument
43-101.
The surface program core is HQ size, equalling 2.625 inches in diameter.
The core samples are collected by Bonanza personnel at the drill for each
drill hole. All of Bonanza's facilities are secure, inside the fenced
compound. The core is transported to Bonanza's core processing facility on
site at Copperstone by Bonanza personnel.
The core is then logged for recovery and other geotechnical features, prior
to being sawed lengthwise in half by Bonanza personnel. Individual core
samples are selected on a geological basis to characterize the gold
mineralization associated with various rock types, alteration types and
structural horizons. Subsequent to sawing and sampling, the remaining half
core is geologically logged and stored on site as reference samples.
Assay sample sizes average 5.5 pounds for the surface drilling. The core
samples are bagged, labelled and tied at the Copperstone project site by
Bonanza personnel. Geologic information is recorded on standardized sample
description forms which included colour, rock type, alteration, mineral
species and abundance. Samples are stored in a secure facility at the
Copperstone project site. Bonanza personnel transport the samples to the
air freight desk of America West Airlines at the Lake Havasu City, Arizona
airport.
America West Airlines transports the samples to the airport in Reno, Nev.
There, representatives of American Assay Laboratories (AAL) in Sparks,
Nev., receive the samples and take custody of the samples. AAL is ISO/IEC
17025 certified and has successfully completed Canadian proficiency testing
(CCRMP).
At the AAL laboratory, the core samples are dried, crushed to minus-10
mesh, pulverized to minus-150 mesh, split to 1,000-gram pulps and fire
assayed for gold three times using two-assay-ton fire assay charges with a
gravimetric finish. Reported gold grades are the average of these three
assays for each sample. A total of 52 core samples were assayed in
triplicate for this hole. There is good correlation between the triplicate
assays. All samples greater than 0.100 ounce per ton, standards and blanks
are routinely submitted to additional labs for verification. An additional
routine four standards were inserted for assay for the drill hole announced
here.
Check assays are routinely submitted to BSI-Inspectorate, Sparks, Nev., and
Chemex Labs, Sparks, Nev., for two- or five-assay-ton gold analysis. Both
labs are ISO 9002 certified. Delivery of the samples to the check labs is
done by Bonanza personnel.
Additional information about Bonanza can be obtained at
www.americanbonanza.com.
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