We all know that reactivated volcanism may dismantle convection cells of shallow hydrothermal activity (which is a very reasonable idea), but can anyone provide compelling evidence, geochronoligic or else, that supports the idea?
Hi Antoni
My limited experience is mostly from the Andes of course but the truth is that at least high-sulfidation deposits tend to be emplaced at the end of magmatic episodes or post-magmatic (we wrote a review covering this published in OGR in 2015). Now, I don't know if the evidence is simply lost or covered in cases where magmatism post-dates HS mineralization. I am aware of one example, La Coipa, where dacitic flows cover alteration and mineralization and which are close in age. Geochron does not permit resolving your question whether or not the volcanism actually terminated the hydrothermal activity.
Yes, it is as I feared... Same thing in the large epithermal deposits on the southern border of the Mexican Altiplano. Let's hope that high-resolution geochronology may help to shed some light on the matter. Thanks!
Hi Antoni,
I started working on the large epithermal Hg-Sb deposits of the Amiata volcano in Italy (ca. 300 ka in age). These are historical deposits for which lots of geological and geochemical data are already available. For these deposits, all data exclude any volcanic activity postdating ore deposition, so I can only agree with Thomas. However, these might not be the type of epithermal deposits you are interested in ... and they are not classic HS
Dear Antoni,
What I have is some publications containing geochronologic data about volcanism postdating ore epithermal deposition in the San Luis Tertiary Volcanic Belt of Sierras Pampeanas in Argentina. These are all belonging to the same Mio-Pliocene magmatic event. However, I´m not sure if this is "compelling evidence"... Please, let me know if this might be useful to you, in which case I can provide the info. Rgs,
I was asking this because I've just interpreted a case of the ceasing of hydrothermal activity as not having anything to do with the post-dating volcanism despite being relatively close in age, and was wandering whether anyone had faced a similar case that could be interpreted otherwise. In principle, I wouldn't mind that it were a HS deposit, as the question relates to disturbing or "blowing up" firmly established convection cells.
Most epithermal deposits may last 1 to 2 m.yr. or less, but those that last longer may show volcanism/subvolcanism temporally intercalated with hydrothermal activity, in cycles, and I wonder the consequences for ore deposition in such cases, particularly in comparison with one-cycle cases...
Thanks for the heads-up about Monte Amiata!
Hi again,
The evidence I have in the papers that I mentioned before it´s in the line of what you write about in the previous post. I mean, hydrothermal and volcanic activity intercalated along about 4 m.y., in varoius magmatic-hydrothermal pulses, which I consider genetically related to a unique event.
Dear Antoni
Yes the lower temperature and salinity values are an important evidence.
I can say that the last hydrothermal activity is enrichment of silisification and mineralizations related to silis-rich hydrotermal fluids. The oxygen isotope values close to meteoric origin fluids. The values support the epithermal stage.
Best wishes
Leyla Kalender
Yo can find the evidence for hydrothermal activity in epithermal deposits via fluid inclusion (Microthermometry measurements) and stable isotope study.
Silica rich solution is evidence for hydrothrmal fluids, then silicificayion should be investigated. microthermometry can also used for investigated the fluid type and origin. Accordingly, salinity and temperature of fluid can easy to be determined.
No, that's not what I meant: my interest lies in the possibility that a reactivation in volcanism (or shallow hypabyssal activity) might have dismantled hydrothermal cells altogether. The process is conceptually clear, but evidence for its occurrence is not necessarily so.
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