RBK : Chirano Gold Project - Ghana-Bankable Feasability Update
ASX Report
12:14:0223 27/11/2002 Issuer: RBK
RED BACK MINING NL 2002-11-27 ASX-SIGNAL-G
HOMEX - Perth
+++++++++++++++++++++++++
CHIRANO GOLD PROJECT - GHANA
* Gold resources increased to 2.05 million ounces (30.4 MT @ 2.1 g/t)
* Chirano ore reserves to be published in mid December, following
completion of Bankable Feasibility Study ("BFS")
* Metallurgical testwork completed confirming amenability of Chirano
ore to treatment using conventional carbon-in-leach flowsheet
* Recoveries of 95% achieved from oxide material, 91% from primary
material and 35-40% by gravity separation
* BFS geotechnical study confirms no structures affecting pit wall
stability with average pit wall angles of 58 degrees in primary zone
RESOURCE INVENTORY UPGRADE
Based on results of the 13,633m drilling program at the Chirano Gold
Project, completed as part of the Bankable Feasibility Study ("BFS")
during the period May-October 2002, consultants RSG Global Pty Ltd
("RSG") has estimated a new Measured, indicated and Inferred Resource
of 30.4MT grading 2.1g/t for 2,051,000 ounces. This represents a 10%
increase in the Resources announced in May 2002.
The new Chirano resource comprises:
RESOURCE CATEGORY TONNES GRADE G/T OUNCES
Measured 6,940,000 2.6 562,000
Indicated 15,150,000 1.9 944,000
Inferred 8,310,000 2.0 545,000
TOTAL 30,400,000 2.1 2,051,000
Notes:
1. The reported resources are based on a 1 g/t cut off and
an emulation of 5m x 5m x 5m size blocks
2. The tonnage has been rounded to the nearest 10,000
3. All grades have been rounded to the nearest one decimal place
4. All ounces have been rounded to the nearest 1000
RSG has subdivided the resource into oxide, transitional and primary
(fresh or sulphide) with 89% of the resource ounces classified as
primary.
Using a cutoff of 0.8g/t the resources total 37,750,000 tonnes
grading 1.9g/t for 2,262,000 ounces. Using a 1.2g/t cutoff the
resources total 24,480,000 tonnes grading 2.3g/t for 1,840,000
ounces. Ore reserves for Chirano will be published in mid December
2002.
METALLURGICAL AND COMMINUTION TESTWORK
Comprehensive metallurgical testwork undertaken as part of the
Chirano BFS has also been completed confirming the amenability of
Chirano ores to a conventional carbon in leach flowsheet. Testwork
was carried out by Ammtec Limited under the direction of engineering
consultant Lycopodium Pty Ltd.
Gold recovery achieved was 95% for oxide ores and 91% for primary and
transitional ore with typical 35-40% recovery by simple gravity
separation. Taking into consideration power and capital costs the
primary ore recovery was optimised on a relatively coarse grind of a
nominal 106 micron. The reduced grinding requirement will impact
positively on project capital costs.
Bond ball mill work indexes for the primary ore are regarded as
moderate in the range of 12 to 18kwh/t with the project design based
on 15.9kwh/t. Oxide ore is considerably softer ranging from 3 to
9kwh/t. Lycopodium has advised that the SAG and ball mills hold under
option by Red Back (refer ASX announcement 17 October 2002) are
suitable for milling of Chirano ore.
Testwork has also confirmed that the ore exhibits low reagent
consumptions with a total cyanide consumption of 0.5kg/t and lime
0.19kg/t.
These results are considered excellent and confirm results obtained
from the earlier testwork.
GEOTECHNICAL TESTWORK
BFP Consultants Pty Ltd ("BFP") has completed an assessment of
geotechnical aspects of the proposed Chirano open pit mine
development based on the recently completed BFS diamond drilling.
BFP conclude that Chirano rocks are generally strong and of good
quality and that the geotechnical features appear consistent
throughout the area examined. No major structures detrimental to
overall pit wall stability were observed.
BFP recommends 70 degree open pit wall batter angles in primary rock
with 45 degree lay backs in weathered material. Berms should be 5m
wide and spaced 20m apart. This translates to an overall pit wall
slope angle of 58 degrees in fresh rock and 40 degrees in the
weathered profile.
Application of the steep BFP parameters to the pit designs will
minimise strip ratios and maximise the economic recovery of gold from
the pits.
R Ashton
MANAGING DIRECTOR
FOOTNOTE:
The resource estimate for the Chirano Project has been categorised
based on the September 1999 edition of the Australasian Code for
Reporting of Mineral Resources and Ore Reserves (The JORC Code). The
resource estimation study has been carried out jointly by Brett
Gossage, Manager of Resources at RSG Global, and James Ridley, a
Senior Geologist with RSG Global, who are both Corporate Members of
the Australian Institution of Mining and Metallurgy, and are defined
as "Competent Persons", as detailed in the JORC Code. Mr Gossage and
Mr Ridley consent to the inclusion in this report of the resource
data in the form in which it appears
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