BajaNews - 3-9-2006 at 05:21 PM
http://www.mineweb.net/co_releases/961555.htm
09-MAR-06
Baja Mining Corp. (the ?Company?) is pleased to provide a further update on the Test Mining Program currently underway on site at El Boleo
Copper-Cobalt-Zinc-Manganese
Project in Santa Rosalia, Baja California Sur, Mexico. John Wyche, Mine Designer for the El Boleo Project Test Mine, of Australian Mine Design and
Development (AMDAD), provides the following update:
The underground mining trial at the Boleo Copper Cobalt Project has been extended into March 2006 to allow expansion of the pillar extraction area.
The mineralised manto, or seam, being mined averages 2.5 metres in height. By the end of February 2006 pillar extraction by continuous miner had
opened a stope area measuring 40 metres by 18
metres, or over 700 square metres. By the end of March 2006 this will be expanded to an area of 37 metres by 48 metres, or nearly 1,800 square metres.
Over 3,000 metric tonnes of ore will have been mined from the pillar area. In addition over 250 metres of access and geotechnical monitoring roadways
will have been driven, all within ore.
The mining trial was designed to provide geotechnical and operational information to guide design of a full scale underground mine capable of
producing over 2.5 million
tonnes per year. This style of mining relies on controlled collapse of the seam roof in the mined out areas so that the broken rock in the collapsed
zone can take the weight of the
overlying strata. Ground movement monitors have been installed around the stope area and on the surface above it to track subsidence of the roof
through to the controlled
failure stage. This information will form the input for numerical analyses of the mine roof, openings, and pillars at the scale required for full
production. Although the stope
area mined to date is small the first stages of controlled collapse are already being observed.
Following a series of delays caused by equipment problems which were unrelated to the mining conditions, mining is now progressing rapidly and it is
expected that the mining
component of the trial will be completed during March 2006. Most of the controlled roof collapse within the stope area should occur in this period but
it may continue for several
weeks so the ground movement monitoring will continue into April 2006.
A great deal of information has been gathered on the mining methods and systems required for efficient, high production underground mining at Boleo:
- The continuous miner registers very low power consumption when cutting the ore so it will be possible to achieve high cutting rates from relatively
small machines.
- The trial site was selected in an area where intensive mining of the high grade base of the manto had been conducted during the earlier years of
last century. However, after mining over 300 metres of access, monitoring and stope roadways through old mine openings, stope fill and undisturbed
ground the trial has only been delayed once by ground conditions directly attributable to the old workings.
This was four metre wide section at the junction of two old drives. One day was lost supporting through the area and that section of the stope was
completed without further delay.
- Numerous pieces of support timber from the old workings have been picked up by the continuos miner but they are all so aged that they crumbled.
There was a concern that the old timbers could have jammed in the miner or caused tears in the conveyor belts but this is no longer considered a
problem.
? Immediate roof conditions have been observed in detail in the collapsed stope area and in several small failures in the access roadways. By
understanding more about the occurrence of low angle faulting in the roof strata, which is prevalent throughout Boleo, it has been possible to plan
roadway widths and rock bolting patterns that the provide good stability.
? Trials with different drill steels and bits have greatly reduced rock bolt installation times in the relatively soft roof strata.
? Testing of different methods of handling the clay rich ore has offered solutions to problems with clay build up on the continuous miner chain
conveyor. This is a common problem with clays but the information gathered allows design of
suitable loading, haulage and handling systems.
? The ore has a high inherent moisture and raises no dust during cutting so there is no need for water dust suppression which could have caused
problems in the high
clay environment.
One of the biggest changes suggested by the trial to date comes from the success in mining through the old workings. Prior to the trial the production
mine was being planned around shortwall panels to provide support through loose ground in the previously mined areas. However it appears that
subsidence through the old workings has compacted the clay rich manto and restored some competence to the mining horizon. This, and the potential for
high cutting rates, enables the mine planners to consider more flexible and lower capital cost mining systems such as room and pillar using mobile
roof supports.
Following completion of mining and geotechnical monitoring, geotechnical analyses of the proposed mining systems will be conducted through April and
May. A mine plan will then be developed through the middle of 2006 to define the detailed mine layouts, equipment fleet, workforce, production
schedule and capital and operating cost estimates.
[Edited on 3-10-2006 by BajaNews]