Greystar's Angostura at 11.55 million ounces Au M+I
2008-12-09 02:54 MT - News Release
Mr. David Rovig reports
GREYSTAR INCREASES ITS GOLD RESOURCES (M&I) BY 13.8% AT ANGOSTURA
A new National Instrument 43-101-compliant mineral resource estimate for Greystar Resources Ltd.'s wholly owned, multimillion-ounce Angostura gold-silver project in northeastern Colombia has increased the measured and indicated resource estimates by 13.8 per cent to 11.55 million ounces of contained gold.
HIGHLIGHTS
Resource Contained gold Contained silver Gold Silver
category (thousand ounces) (thousand ounces) (g/t) (g/t)
Measured 3,736 20,000 0.78 4
Indicated 7,813 41,000 1.34 7
Measured and indicated 11,549 61,000 1.09 6
Inferred 3,472 18,000 1.19 6
Cut-off grades: 0.3 g/t Au for oxides; and 0.45 g/t Au for sulphides
Highlights:
Measured and indicated mineral resource estimate of 11.55 million ounces of gold and 61 million ounces of silver;
Average gold grade of 1.09 grams per tonne (g/t) in the measured-plus-indicated category and 1.19 g/t in the inferred category;
New resource estimate includes the results from 870 drill holes totalling 277,000 metres of drilling, completed until May 31 of this year, including the results of 153 holes and including the 32,557 metres drilled after the cut-off date for the December, 2007, resource study.
"The new results show the anticipated positive impact of the infill drilling program which provides a basis of the conceptual mine plan for the first phase of the feasibility study phase I," said Greystar's executive vice-president, Frederick Felder, PGeo. "Since our December, 2007, mineral resource estimate, we have updated the database with assay results from an additional 32,557 metres of diamond drilling in 153 holes and that has resulted in a 13.8-per-cent increase in measured and indicated gold resources from 10.15 million ounces to 11.55 million ounces while inferred gold resources stayed basically unchanged at 3.47 million ounces."
ANGOSTURA GOLD AND SILVER RESOURCES
Measured mineral resources Indicated mineral resources
Tonnes Au (oz, Tonnes Au (oz,
(thous- Au thous- Ag (thous- Au thous- Ag
ands) (g/t) ands) (g/t) ands) (g/t) ands) (g/t)
Oxides 49,620 0.63 1,007 5 37,246 1.05 1,258 7
Sulphides 99,280 0.86 2,729 4 144,760 1.41 6,555 7
------- ---- ----- - ------- ---- ----- -
Total 148,900 0.78 3,736 4 182,006 1.34 7,813 7
Measured and indicated Inferred mineral resources
mineral resources
Tonnes Au (oz, Tonnes Au (oz,
(thous- Au thous- Ag (thous- Au thous- Ag
ands) (g/t) ands) (g/t) ands) (g/t) ands) (g/t)
Oxides 86,867 0.81 2,265 6 6,241 1.33 266 9
Sulphides 244,040 1.18 9,284 6 84,539 1.18 3,205 6
------- ---- ----- - ------- ---- ----- -
Total 330,907 1.09 11,549 6 90,779 1.11 3,472 6
Mineral resources that are not reserves do not have demonstrated economic viability. An inferred mineral resource is that part of a mineral resource for which quantity and grade can be estimated on the basis of geological evidence and limited sampling and reasonably assumed, but not verified, geological and grade continuity. An indicated mineral resource is that part of a mineral resource for which quantity, grade or quality, densities, shape and physical characteristics, can be estimated with a level of confidence sufficient to allow the appropriate application of technical and economic parameters, to support mine planning and evaluation of the economic viability of the deposit.
Completed by Greystar staff, headed by Ing. Giovanny Ortiz, Greystar's Datamine specialist, and under the overall supervision of consulting company Metalica Consultores SA from Santiago, Chile, the current estimate includes the data of 277,000 metres of diamond core drilling distributed in 870 holes drilled up to the end of May, 2008. Also included are the results from the 25- and 12.5-metre-spaced underground horizontal drill program completed in 2008 that was designed to better define in detail a core area of the deposit. The Angostura deposit resource estimate contains 3.7 million ounces of measured and 7.8 million ounces of indicated gold along with 20 million ounces of measured and 41.1 million ounces of indicated silver contained in 330.9 million tonnes in both categories grading 1.09 grams gold per tonne and 5.8 grams silver per tonne. In addition, another 3.5 million ounces of gold and 17.6 million ounces of silver are estimated within an inferred resource of 90.8 million tonnes grading 1.19 grams gold per tonne and six grams silver per tonne.
The reported global estimate has not been constrained by the consideration of mining recovery and dilution parameters, but it has been based on cut-off grades of 0.3 g/t and 0.45 g/t gold for oxide and sulphide resources, respectively. The cut-off grades have been changed from past estimates, which used 0.4 g/t and 0.55 g/t gold, respectively. The change in the cut-off grades reflects using a higher gold price of $650 per ounce compared with the $500 per ounce of gold that was used in some of the previous studies.
Resource estimation was undertaken in compliance with CIM mineral resource and mineral reserve definitions that are referred to in National Instrument 43-101, standards of disclosure for mineral projects. A location map of the Angostura drilling, along with a map of the underground tunnel work, and an updated concession map can be accessed from our home page link at Greystar's website.
Estimation parameters
The December resource study is based on an updated 3-D geological and mineral model, and includes all of the technical data available as of May, 2008, including core assays from 277,000 metres of drilling and 1,464 muck samples from the Perezosa exploration tunnels and crosscuts. The resource model also includes a total of nearly 8,400 specific gravity measurements. This is of importance as higher-grade mineralization on average has from 10-per-cent and 15-per-cent higher density.
The current model has used structural trend surfaces that follow the interpreted veins throughout the deposit. The trend surfaces guide the direction of the three axes of the search ellipsoid used for grade interpolation on a local scale and assure that the geological influence on the grade interpolation is preserved.
All gold assay data were split into two populations, high grade and low grade, generally using a threshold of five g/t gold. Both populations were composited to intervals of 1.25 metres, and grade capping was applied to the composites. Capping levels for the high-grade population was 90 g/t for the Veta de Barro Este area, no capping was used for the Veta de Barro Oeste area, and 65 g/t gold for the central area. The low-grade composites were capped at 3.7 g/t gold for Veta de Barro Oeste area, 4.1 g/t gold for the Veta de Barro Este and 3.8 g/t for the central area. The capped 1.25-metre composites were recomposited to 6.25 metres for grade interpolation of the low-grade population, while the capped 1.25-metre composites were recomposited to up to 10 metres for the grade interpolation of the high-grade population.
The block model uses regular blocks of 6.25 by 6.25 by 6.25 metres. Search distances for the probability and grade interpolation are supported by variography results. The probability of a block to contain high-grade mineralization was interpolated using an indicator approach which applied a floating ellipsoid with radii developed for six different domains. The probability interpolation used an inverse distance to the 12th (ID12) power to minimize undue grade projection. As a result of the probability interpolation, each block contains an estimate of the volume of high-grade and of the volume of low-grade mineralization.
The grade interpolation was undertaken weighing the grade information by the inverse of the square of the distance to the block being estimated (ID2). In a first interpolation step, the low-grade material in each block was interpolated from surrounding low-grade composites using ellipses for the first search with a radius between 50 to 75 metres in strike and dip, depending on the domain, and a fixed 6.25 metres for cross strike in both searches; while the second search was two times the first one. The grade of the high-grade material in each block was interpolated from surrounding high-grade composites using the same search ellipsoids as were used for the probability interpolation. A second-grade interpolation step followed for which the ellipsoid axes were doubled. Blocks beyond the reach of this larger search were not estimated. To avoid over estimating of high grade, a 30-metre radius was used to restrict the impact of the high grade.
The estimating method described has not been changed from the December, 2007, study, with the input and supervising of consulting company Strathcona Mineral Services Ltd. of Toronto. Only some parameters were updated according to the new data added.
In-pit resource
The mine design developed by Metalica Consultores in the feasibility study phase I has obtained an operational pit that contains the following resources using different cut-off grades, including measured, indicated and inferred classes. Silver values have not been accounted for in the cut-off grades.
Metalica obtained the pit using a gold price of $650 (U.S.) per ounce, and a silver price of $9 (U.S.) per ounce. The operational costs were recalculated, and new geotechnical parameters were introduced.
ANGOSTURA RESOURCES INSIDE OPERATIONAL PIT, METALICA 2008
Sulphides Oxides
Tonnes Au (oz, Tonnes Au (oz,
Cut-off (thous- Au Ag thous- (thous- Au Ag thous-
grades Au (g/t) ands) (g/t) (g/t) ands) ands) (g/t) (g/t) ands)
Oxides 0.4 133,863 1.48 7.41 6,365 61,391 1.09 6.88 2,160
Sulphides 0.5
Oxides 0.3(i) 156,984 1.33 6.79 6,717 88,263 0.87 5.87 2,460
Sulphides 0.45(i)
Oxides 0.2 185,005 1.19 6.20 7,100 127,070 0.68 4.94 2,768
Sulphides 0.4
Total
Tonnes Au (oz,
Cut-off (thous- Au Ag thous-
grades Au (g/t) ands) (g/t) (g/t) ands)
Oxides 0.4 195,254 1.36 7.24 8,525
Sulphides 0.5
Oxides 0.3(i) 245,247 1.16 6.46 9,177
Sulphides 0.45(i)
Oxides 0.2 312,075 0.98 5.69 9,868
Sulphides 0.4
(i) Resource estimate with the same
parameters used to calculate the global
resource estimate outlined in this press
release
Compared with the seven million ounces of gold within the pit obtained by the 2007 Hatch study, the new pit is significantly improving the gold content due to the eastern pit geometry, which was optimized by the new resources found in Los Laches and La Alta Este and also by reducing the cut-off grade. The inferred resources within the pit represents, for the first (higher) cut-off marking, 6.7 per cent of the total tonnage and 12 per cent of the gold ounces; the second cut-off represents 5.9 per cent and 11 per cent, respectively, while the third (lower) cut-off represents 5.2 per cent and 10.4 per cent respectively. Fifty additional drill holes representing 22,374 metres have been completed since June, 2008, and will be added to the final resource evaluation to be developed in 2009 for the definitive feasibility study (phase 2).
The average depth (vertical) of the drilling is from 270 to 300 metres to 430 to 480 metres. The more shallow coverage is in the peripheral areas such as Los Laches, La Alta East, the southern limits of El Silencio, Veta de Barro, whereas in the central part of the deposit, greater depths have been tested from underground.
Fifty additional drill holes representing 22,374 metres have been completed since June, 2008, and will be added to the final resource evaluation to be developed in the second half of 2009 for the definitive feasibility study (phase 2).
The potential impact on the mineral resource estimate of environmental, permitting, legal, title, taxation, sociopolitical, marketing or other relevant issues has been previously discussed in the Strathcona technical report dated Aug. 30, 2006.
Review by qualified person, quality control and reports
The 2008 resource estimate was prepared by Greystar staff under the oversight of Marco Alfaro Sironvalle, mining engineer of Metalica, and an independent qualified person as defined by National Instrument 43-101. The standard of reporting is National Instrument 43-101 compliant and a technical report detailing the resource estimate will be filed on SEDAR within 45 days.
The results of this press release have been reviewed and verified by Mr. Felder, PGeo, a qualified person for the purpose of National Instrument 43-101, and guidance note for mining, oil and gas companies issued by the London Stock Exchange in respect of AIM companies, which outlines standards of disclosure for mineral projects. Mr. Felder has over 30 years of mineral exploration experience, and is a member in good standing with the Association of Professional Engineers and Geoscientists of British Columbia.
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