Empirical geotechnical improvements for low-angle narrow vein gold mining through modified long hole methodology - experiences from Pilar de Goiás, Brazil
Jaime Andres Corredor Herrera1; Jairo Henrique Da Silva1; Natalya Raquel Medeiros Leitão1; Paula Pertile1
1 Pilar de Goiás Desenvolvimento MIneral; Brio Gold Inc.
Resumo
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 orebody, 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. The Brazilian Pilar de Goiás mine site is located in the central region of Goiás State, where regional tectonic models locate the mobile belt and thrust belt as the principal geological feature representing an extensive metamorphic greenstone belt as part of Neoproterozoic Orogeny. The Pilar belt is an extensive foliated metamorphic sequence of alternated meta sedimentary and meta volcanic units, which serves as the host-rock for three individual gold bearing laminated quartz regional fault fill veins, representing the most important targets for the exploration and production of the mine sites. 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 orebody inclinations dip varying from 18 to 30°. Detailed underground geological structural modelling 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 hangingwall. This included 3-2 to 2-1 staggered drilling patterns as a function of orebody 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
Palavras-chave: Narrow Vein; Long Hole ; Greenstone Belt; Schist; Low Angle