Narrow vein deposits are highly sensitive to dilution events during extraction stages. This is due to several geological features such as lithology, structural setting, ore thickness or inclination of ore body, therefore conditioning the effectiveness of its extraction methods.
This work reviews the results of continual improvements in extraction methods in a foliated low-angle narrow vein ore deposit in the Brazilian Pilar de Goiás gold mine, through low-angle open stope design.
Since long hole mining was proposed, the establishment of stable span dimensions became a critical aspect for validation and operability of the extraction method. The proposal was initially tested in several panels with ore body inclinations dip varying from 18 to 30°. Detailed underground geological structural modeling allowed the geotechnical department to estimate stable hydraulic radii (HR) obtained empirically using Mathews stability graphs.
As a complement to this approach, several drill and blasting procedures were proposed to improve the final hanging wall. This included 3–2 to 2–1 staggered drilling patterns as a function of ore body width. The aim was to reduce blast damage as much as possible in order to obtain maximum recovery rates of selective high-grade ore production with minimum dilution.
Preliminary results showed three main controlling factors to take into account for successful implementation of a modified low-angle narrow vein long hole stopping method:
panels must be projected for inclinations above 25° to optimize fragmented ore removal from the open stope using water jets;
increasing the panel length and maintaining its stability when the hanging wall presents the strongest rock type; and
correct rib pillar positioning related to the main structural features during preparation stages require strict controls to avoid future unstable roof stope complications as production blasting is being executed.