Prospect trench in the Albite Hills.
We soon drove to the upper bench of the McArthur Mine - we were there to learn the detailed mapping method called "The Anaconda Method." The Anaconda Method was designed by Anaconda geologists in the 1960's. It's a very specific and detailed form of mine mapping, designed in part for mapping porphyry copper deposits, which can imaprt a lot of information on one sheet of paper. It can be used for underground, open-pit mines, trenches, and roadcuts, and can be adapted for any type of deposit or area. I could find very little reference to this particular method online; we were given a 1997 handout printed by Marco T. Einaudi of Stanford, entitled Mapping Altered and Mineralized Rocks: An Introduction to the "Anaconda Method." The handout is as detailed as the method!
Each person mapped a 100 meter length of bench face at 1 cm = 2 m, with a 100-meter tape strung out along the bottom of the bench face. Mapping, as in underground mapping, is done at waist high, or some similar arbitrary height.
By the end of the day, standing in front of the bright, reflective bench face, the sun had become quite warm - almost hot - warm enough that I retreated to the vans in the afternoon to find some shade.
Day 3: Mapping is done for the day, and geos have gathered at van #1 for the afternoon wrap-up and discussion. Questions:
- How much sulfide and copper was in the rock originally and how much is there now?
- Where did the copper oxides [and carbonates and other non-sulfide copper] come from?
- What were the fluids like, and how can we tell?
Some answers were forthcoming upon discussion, and my field notes are quite messy!