Hi EZ,
It’s a shame that pictorial you are referring to is not available on line any longer. It took Greg Corbett’s model which you posted and overlaid it with specifics to the ADL. For instance, that blue area of skarnified limestone was labeled “LDM”. Corbett is a brilliant guy from NSW, Australia. This model, however, doesn’t do justice to the differential between epithermal and mesothermal vein systems. Meso’s are rare enough that they often don’t get mentioned in the renditions of classic porphyry models like those of Corbett or Sillitoe. (I’ll warn you that studying Corbett’s lectures on line will drive you nuts because the camera is always on him while he’s wielding his laser pointer at various slides, but he really is good.)
The ADL Mining District is a smorgasbord. It has all of the various adnexal structures seen in the classic copper porphyry model. Where it stands out head and shoulders above most is the presence of a vast low sulphide mesothermal vein system. The “VAST” is important and was corroborated by the trenching program of Auryn, the “LOW SULPHIDE” is important, the “MESOTHERMAL” is beyond important and the presence of a true “VEIN SYSTEM” is important. Almost all gold-bearing lode deposits involving veins is of an “epithermal” nature. These are wonderful and they account for a lot of the gold production worldwide. The analogy often used is that they are like apple orchards whereas the much rarer MESOTHERMAL VEIN SYSTEMS are more analogous to a redwood forest. The meso’s often extend super-deep (often to about 1,500 meters) and more importantly they tend to widen with depth and the grades often tend to improve with depth. The economics of meso’s can blow away that of the epi’s by lightyears.
Auryn management has been holding off on telling us the results of Richard Sillitoe’s 4-and-a-half-day visitation of the ADL. We knew that ACA Howe suggested that we might just be sitting on a mesothermal deposit. Us geo-geeks have been sitting on pins and needles waiting to see if Sillitoe came up with the same diagnosis i.e. a redwood forest and not just an apple orchard. It appears that Auryn management didn’t want to reveal Sillitoe’s diagnosis until they corroborated it via sampling “Shaft #1” at the old Fortuna Mine. Management’s recent update stated that the widths and grades are indeed improving with depth and that we are indeed sitting on a mesothermal vein system. Then they said basically that, oh, by the way, Sillitoe concurs with ACA Howe’s theory.
This is not rocket science. The meso’s form much deeper than the epi’s. Down deep, both the PRESSURES and the TEMPERATURES are much higher than that found near surface. If you start with a half of a meter wide fault or crack in the rocks above a magma chamber, the explosivity down deep can make that a 2-meter-wide crack/fault in a heartbeat. As the hydrothermal fluids and gases rise and cool both the PRESSURES and TEMPERATURES drop. Up near surface where the epi’s hang out, there’s no more lateral pressure left to widen that 0.5-meter-wide fault/crack. Thus, these meso’s widen with depth.
Meso- systems are not that tough to diagnose. Picture the hydrothermal fluids ascending out of a magma chamber as being on an elevator. If the hydrothermal fluids ascending out of a magma chamber are 300-degrees Celsius, and they depressurize and cool as they rise, the molten rock components will solidify when they reach a level that matches their melting point. They’ll exit this elevator as solids and stay at that level. Moly is famous for having a very high melting point. It’s the first guy off of the elevator down low.
So, meso’s are going to be found in association with rock types with high melting points. We know what the melting points of various rock types are. This is why the ACA Howe’s and Sillitoe’s of the world can say, yep you have a mesothermal deposit. It’s pretty much a given that the veins are likely to widen with depth and extend way down deep. This is just physics.