A question in my (non-geologist) mind has been how precious and semi-precious metals' concentration relates to copper concentration in porphyry deposits. Gold, silver and molybdenum may or may not be present in copper porphyry deposits in economically useful concentrations. If present, how do they track copper concentration in variable grades?
I spent some time this weekend reading up on copper porphyry geology and published resource reports from other projects in the Americas, selecting four different copper porphyry resources reports that are quite some geographical distance apart to see what they found where the copper resource grade shows variability. From this limited review, it appears that as copper concentration increases within the ore grades, the concentration of gold increases as well. See references below. I didn’t do a deep dive looking into every combination of precious and semi-precious metals along with copper (such as silver and molybdenum). These four projects are primarily copper and gold deposits.
The Exall data referenced in an earlier post is intriguing. But we won’t know for sure what San Tomas reveals until confirmatory drilling data is published. I am looking forward to seeing if the Cu / Au relationship identified on the other four projects holds true here. It seems like a reasonable presumption. This is an exciting time to watch this project proceed.
Azucar El Cobre Project (Sonora, Mexico) NI 43-101 Technical Report
https://azucarminerals.com/el-cobre-project/technical-reports/
This project includes five Cu-Au porphyry deposits.
See Pages 46 and 47.
Cordoba Minerals (Colombia) NI 43-101 Technical Report
https://www.cordobaminerals.com/assets/docs/2019-07-29-san-matias-pea.pdf
This project includes Cu-Au-Ag porphyry deposits.
See Pages 157 and 165.
Cotabambas Copper-Gold Project (Apurmac, Peru) NI 43-101 Technical Report
https://www.panoro.com/site/assets/files/3540/cotabambas-copper-gold-project-national-instrument-43-101-technical-report.pdf
The Cotabambas Property hosts Cu-Au porphyry mineralization that is part of the Eocene-Miocene porphyry belt of Southern Peru.
See page 10-3.
Technical Report on the Los Helados Porphyry Copper-Gold Deposit (Los Helados, Chile)
https://ngexminerals.com/site/assets/files/113177/los_helados_standalone_2019_43-101_final_listing_applic.pdf
The Los Helados deposit is classified as a porphyry Cu–Au system.
See page 7-14.
“Copper grade increases downwards, either in the lower parts of the sericitic zone or in the underlying chlorite–sericite alteration zone, and elevated grades are maintained into the potassic alteration zone. Within the central part of the breccia body, consistent grades on the order of 0.5% Cu and 0.2-0.3 g/t Au in the core zone are flanked by domains of ~ 0.3-0.4 % Cu and 0.1-0.2 g/t Au. High grade zones exceeding 1% Cu and 1.5 g/t Au are found locally. Although Cu grades typically diminish towards the bottoms of the deepest holes drilled to date, there is an exception in that drill hole LHDH34 encountered some of the better grades of the deposit (>1%Cu and >1.5 g/t Au) in a breccia body at 900 metres.”