Article on Red Lake Geology Found article that mentions 8 Zone
Geology
Gold mineralization in Red Lake is considered to be orogenic (AKA greenstone) in nature. These deposits form when rocks, typically basalts, are metamorphosed in orogenic (mountain-building) events. The temperatures and pressures produced by these events causes the rocks to ‘sweat’, releasing Au-bearing fluids which migrate along geologic structures such as faults, folds, and shear/strain zones to form rich, nuggety Au-bearing quartz and carbonate veins.
Nuggety gold in quartz from the Red Lake Mine. Most of the Au in the Red Lake camp is found in quartz-carbonate veins hosted in metamorphosed basalts of Balmer assemblage, although some is also found in granites and ultramafic rocks. Gold in the newly discovered Dixie Project 25 Km south of Red Lake is found in quartz veins in basalt, but also scattered in felsic volcanic rocks in a mineralization style similar to the world class Hemlo deposit, but which is still not well understood.
Red Lake’s Au is extremely old, dating to approximately 2.72-2.71 billion years ago. This extreme age means there’s been plenty of time for metamorphism, faulting, igneous events and more to disrupt the original geology. Many rich ore zones in Red Lake are abruptly terminated by tiny, nearly invisible, ‘black line’ faults which may displace the ore 100’s of meters and leaving few clues as to if or where a geologist should expect the ore to continue. Some ores may also have been partially moved and re-concentrated by hydrothermal fluids into later generations of veins.
To make matters worse, Red Lake Au is known to be particularly nuggety and unevenly distributed on a fine scale. One drillhole may encounter high-grade Au, while another less than a meter away may hit little to no Au. Copious amounts of drilling and large bulk samples are required to determine the true amount of Au present.
Although ground conditions for mining are generally good, this is not always the case. Legend has it that when miners tried chasing the particularly rich Au of Madsen’s 8 zone, they found the altered ultramafic rocks so soft that they actually deformed under the pressure of the overlying rocks enough to trap machinery underground.