Dear Mr. Pelletier,

it strongly depends on how metamorphism is related in time and space to the presence of HS type gold deposits. I published a  metallogenic study (DILL, H.G (1998) Evolution of Sb mineralisation in modern fold belts: Comparison of the Sb mineralisation in the Central Andes (Bolivia) and the Western Carpathians (Slovakia).- Mineralium Deposita, 33: 359-37), comparing the plate tectonic setting in the Bolivian Andes with the Western Carpathians in Slovakia. To give a rough scheme along a NNW-SSE transect the metallogenic setting is as follows. The metamorphic core zone of the Central European Variscides of Precambrian to Paleozoic age synonymous with Meso-Europe is located north of the Western Carpathians synonymous with Neo-Europe. The latter crustal section gave host to HS- and LS-type gold deposits (see DILL, H.G., SACHSENHOFER, R.F., GRECULA, P., SASVÁRI, T., PALINKAŠ, L. A., BOROJEVIĆ-ŠOŠTARIĆ S., STRMIĆ-PALINKAŠ S., PROCHASKA, W., GARUTI, G., ZACCARINI, F., ARBOUILLE, D., and SCHULZ H.-M. (2008) Fossil fuels, ore – and industrial minerals .- In: T. McCann (Ed.), Geology of Central Europe, Geological Society of London, Special Publication, London, 1341-1449 . Both parts the metamoprhic core zone, albeit of different geodynamic settings are connected with each other by plate tectonic processes. To illustrate this spatial relationship of metamorphic core zone (Bohemian Massif) and newly formed HS-and LS deposits I attach a file displaying both metallogenic provinces juxtaposed for comparison with your setting under consideration.

Best regards

Harald G. Dill

Dear Harald Dill, THANKS for the pdf. Very impressive in its simplicity for better understanding. As you may know, I am working on a new concept for the genesis of the epigenetic emplacement of the Kupferschierfer metals & corgs. Question: Have you given consideration to a metallogenetic dynamic cross section through the late Permian situation at the northern margin of the Middle European Cystalline Zone?

Best from Tucson, Arizona & GLÜCKAUF!

VOLKER

I think for more information you can find from  author K.H.Wedepohl because he working more for geochemistry European copper deposits.

All the best

Dear colleagues,

in the present case magmatic-related Cu concentration is the process which counts. The so-called Cu shales, Cu sandstones or Cu-belt deposits are not to be expected in a geodynamic environment like that (See: Dill (2010) "The chessboard classification scheme of mineral deposits.....).

Best regards.

Hi Mr. Pelletier,

I worked on a gold project in Sonora (Canasta Dorado) near Caborca in 2008 that was hosted in the hangingwall of the La Gloria detachment fault.  The auriferous quartz veins which cut the hangingwall never penetrated into the (fantastically) mylonitized footwall.  Field and core observations suggested that these veins were dilational (possibly en echelon) veins that formed above the detachment fault and were likely syngenetic with extensional faulting.  Although the grade could be good, the ore zones had poor continuity, and because the veins were restricted to the hangingwall, the zone of mineralization was relatively thin.  We never categorized them as 'epithermal', though perhaps they could be broadly considered as such.

After this experience, my bias has become that metamorphic core complexes are not good zones for mineral exploration.  The hangingwall cover rocks are completely detached and disassociated from their footwalls, and therefore the usual vertical conduits of metals and fluids are absent.  Moreover, the rocks at depth (the metamorphic footwalls) are mylonitic mid-crustal rocks exhumed from 10-20 km that were not fertile to begin with.  I don't know if this is a truism for the entire globe, but it is strongly suggested in the belt from eastern California and the Colorado River extensional corridor to western Arizona to northern Sonora.  An exception to this general bias would be where young granitoids intrude the footwall late in the deformational history such that they are relatively unstrained.  But even so, where this is observed (Whipple Mtns, CA, for instance) there are no important signs of mineralization.  Mostly what you do see in these MCC ranges is spotty lenses  of barite-Cu "oxide"-Mn "oxide" (plus neotocite, etc.). 

The better mineralized zones seem to be on the fringes of well developed core complexes, i.e., El Chanate Au deposit, and arguably, the wide zone of porphyry Cu deposits in AZ+Sonora that lie in-board (N. America side) of the belt of extreme extension.  Gold, of course, is spotty throughout the region but only really hangs together to form a signifcant deposit in a few places.

Suerte!

I'm very impressed by your field experience and your synthesis of the area. Your generous answer deserve that I'll tell you the truth about the goal of my question. I just wanted to evaluate how many people are interested and understand the processes needed to generate PCS in large rift, such the Basin and Range. Inspired by Jonathan Nourse, I think that deep lithospheric Jurassic structures has been reactivated during Middle Tertiary extensional regime from Southern California to Northern Sonora.

Since the last years, many epithermal system related to detachment fault (Ada Tepe, Jojoba-Lluvia de Oro, Paradise Peak) or metamorphic core complex areas (Mesquite, Sappes-Viper, Guneykoy) have been discovered. Once again, Sillitoe's team is still ahead of the exploration targets and their understanding of Paradise Peak is impressive (Richard H, Silitoe, Lorson C R, 2016).  With all the work and research, it’s just a matter of time, before we establish the origin of the process that generated these deposits.

Gold occurrences are abundant along the MCC belt, but rare are the significant discoveries. Perhaps, rare are the exploration companies that are going to invest time and effort to understand the origin of the gold. Once again, a lot of precious information will be lost, due to competitive philosophies in the exploration and mining industry. Thanks again for sharing.

Best regards,

Josh