So...has anyone else found a fluidized dacite cemented "tourmaline zebra rock" like this?
I have never heard of such a thing capping porphyry copper systems...tin, polymetallics...yes. But they are not well researched.
The descriptions of fluidized dikes exiting a high pressure center in Peru are good but the system is likely not porphyry copper related...
We drilled into the flanks of this dome on a radial dike exiting the domal bx area and found digenite in rotten pods associated with minor anhydrite at 200 meters probably when we left the lithocap. The fluidized dacite like material on the cliff is the same as what is in my hand from core drilling. The material in my hand runs 0.3-4% cu.
The whole area stands out as a distinct circular mag high so there is magnetite with the tourmaline. For fun I enclosed what looks like sheeted filled black tourmaline/hornfels? veins at 15,000 ft. (4500m) hosted in "chickenwire" foliation. Likely from granitic intrusive activity from below pushing and fracturing the central plug. No I cannot go there and do field work. I do enclose a bit of the same radial dike that provided a commercially small amount of ore grade material.
I cannot help but think some of the prominent repetitive black zones represent chemical fronts...such as found and well described in "zebra rock"...as in the one from India below.
Images from core show possible mafic enclaves and or tourmaline clots hosting chalcopyrite and covellite like blue reflecting material in a matrix hosting coxcombs and terminated quartz xtls.
Interestingly, these tourmaline rich areas seem to represent fluid escape structures from the initiation of subduction in a downgoing slab...tomographically estiated as about 100 km down. There are suggestions high B magmas in the Bonin Island Chain are modern analogues of what we see "dehydrating off" the downgoing slab and escaping the "slab wedge" area. Interesting huh?
So...those tourmaline breccias represent fluids that likely escaped from the zone of slab serpentinization.
Here is a public magnetic map for the area from SEG 2018 showing where the tourmalinized magnetite bearing epithermal to potassic zone exposed domal structure is. Drilling shows there is a modest amount of chalcopyrite/covellite/digenite/bornite associated with it on the flanks. I think it caps a miocene granititic system below. The exposed material is x-cut by veins and dikes but it is generally inaccessible being on a cliff and at 16,000 ft. There are traces of devonian hexagonaria? (or pyrophyllite) to carboniferous pyritiferous micro fossils from core so the setting includes limestone rock but no clear dating of the intrusive yet. Is it Triassic-Choiyoi capping a deeper intrusion? Seems likely. Interestingly, there is a reported slab gap in the area...possibly a window or a tear.
Notice the flat slab area and the bend it makes to return to a steep slope seems to be located right where the so called "slab gap" exists noted above. Note there are a number of nearby stress relief splays that seem likely to be related to changes continued regional transpression and stress accumulation at the edge of the flat slab, deep as it may be. Thus we should expect fluid escape structures, either associated with high confining stress depressurization and formation of "zebra rock" and low confining pressure stress relief as cataclastites sometimes with distinctive "chickenwire" fractures...as below near El Gaucho at what appears to be a vertex where the Domeyko and Elqui Limari structures converge forming a duplex basin adjacent to apparent thin skin detachment fault structures that look like "slippers" decending from high elevations as a set of high wall detachments, block rotations and eastward headwall migration over time. The cataclastites may date choiyoi but they have been seriously disrupted, intruded and even....as described above, tourmaline fluidized from deep high pressure sources...reportedly from serpentine dewatering at depth.
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