FMF - Friends of Minerals Forum, discussion and message board

[Jean Sendero]

Here is another locality question.

The nifontovite that have been coming out of Charcas are from what deposit and Level? I am finding all sorts of information, I suspect not accurate.

Is it from the Rey y Reina Mine, level 16, or from the San Bartolo Mine?

Do we know the name of the mineralized body it was found in? or was it found in a "fault zone" as I have heard? Or do we know the type of geological environment it was formed in and it's associated minerals. I recently acquired one and it has a chalky white coating on it, any idea?

Cheers
Jean

[John S. White]

Peter Megaw will be the one to answer your questions. He has some of the finest crystals of nifontovite to have come from the mine. Perhaps he will post photos?

[Peter Megaw]

Jean and John...buenos dias! When I bought the first lot of these 3 years ago I was told it "probably" came from San Bartolo. As the rest of the pocket was offered incrementally I was told the seller had admitted it really came from Rey y Reina. The "probable" Level 16 attribution stems from recognition that that is where RyR was being exploited at the time. I doubt there is anyone beyond the collector who brought it out who knows definitively where it came from.

This all means we have no direct idea of the environment it comes from. However several of the larger pieces that have emerged have impressions of large danburite crystals in them, so I have to infer that the Nifontovite occurs as a late growth in a danburite vug. Underground exposures show clearly that the danburite forms in vugs between replaced domains and in breccia voids...so it is post (most) sulfide. I say most because I have a huge arsenopyrite crystal group (20 cm across) that overgrew danburite. I doubt there is a fault zone here, but a collapse breccia might be so described by an unsophisticated miner.

Marcus Origlieri has done some analyses on the species associated with and included within the nifontovites. He has identifed bakerite and calcite.

To me one of the most intriguing questions about Charcas is how boron-rich the entire deposit is...danburite and datolite abound with trace but significant nifontovite and bakerite (which may be more common than we realize since it's fine-grained, ugly and easily overlooked). Except for this, Charcas appears to be a typical Mexican skarn-Carbonate Replaceent Deposit. There are minor to modest amounts of B-rich minerals in other skarn-CRD systems in this part of Mexico. Minor danburite at Zimapan, Hidalgo and possibly somewhere near Tamazunchale, San Luis Potosi, (Beals can confirm this); axinite at Fresnillo and Sabinas-San Martin, Zacatecas, and a dubious report of datolite from Guadalcazar, San Luis Potosi. None of the other Mexican CRDs contain more than trace B...beyond trace amounts of tourmaline.

I suspect that there is a borate-rich evaporite deposit in the deep stratigraphic sequence at Charcas and that circulating intrusive-driven fluids entrained brines from those evaporates, creating a hybrid magmatic and sedimentary dervied orefluid. The reports (albeit questionable) of danburite, axinite and datolite in other nearby skarn-CRD systems (Guadalcazar, Tamazunchale and Zimapan) may support this hypothesis. The presence of buergerite (tourmaline) in the tin-topaz rhyolites at Mexquitic, 80 km due south of Charcas may also support this idea. Tin-topaz rhyolites are abundant throughout the region, but B only shows up (or has been identified) at Mexquitic, so perhaps the source zones of the rhyolite flow domes also mobilized B from the sedimentary sequence. I am not aware of borates being reported in the modern evaporites at Salinas, just west of Mexquitic, but there is significant lithium there, suggesting possoble recycling of very light elements from older sources.

The abundant danburite makes Charcas very reminiscent of Dalnegorsk (or vice versa). Anyone know of B-rich evaporites there, or danburite-bearing skarns in Death Valley or other borate-rich areas?

[Peter Megaw]

Whoops...forgot to credit Jeff Scovil for the pictures!

[Jean Sendero]

Great information Peter, thanks.

Interesting that you draw the attention to the possible presence of evaporites burried below in the stratigraphy. This is something I always used, although not B-rich ones, in the recognition of prospective teranes for Sed-Cu and even BHT type mineralization but it never crossed my mind that it may be the case for some HTCRD. Indeed I would expect to see a lot more tourmaline in the overall environment but who knows.

Looking at the specimen, bakerite seems to make sense. But from a more "adventurous" point, I am looking at Sinkankas book and it says that bakerite is quickly dissolved in HCl and Nifontovite is slowly soluble in HCl. Anyone tried to remove the bakerite coating? The water gun is not successful.
Cheers
Jean

[Peter Megaw]

Jean, I am not suggesting your white coating is necessarily bakerite...that has not been tested yet I don't think.

James Lyons has been doing some very interesting regional work in western Mexico recharacterizing what used to be called the Guerrero Terrane as a back-arc basin filled with volcanic debris of "oceanic" origin and with B-rich evaporites. He has used the abundance of tourmaline in mid-Tertiary ore deposits of the region to map out the overall limits of distribution of these only locally exposed volcano-sedimentary rocks. Virtually everything west of Batopilas appears underlain by them. He published a paper in the 2007 AGS Symposium Digest on this work...but has carried it a lot farther.

Are you going to Keystone next week?

This discussion beats "magic merlinite" all hollow

[Jean Sendero]

Chile this afternoon and Keystone next Saturday.

[javmex2]

Hi Peter,
This conversation is very interesting, maybe you can recommend some book that shows maps of mine sites and information on such sites. You are a person with much knowledge, thanks for sharing.

[Peter Megaw]

Javier...buenos dias! There is a recent volume published by the Servicio Geologico de Mexico (SGM)...in Spanish, edited by Kenneth Clark from UTEP...called "Geologia Economica de Mexico" with articles on over 110 different mines and ore deposits around Mexico. It weighs nearly 4 kg and costs around 1000 pesos. I suspect you can order it on-line. You might be able to get a discount if you get it through one of your engineer friends who belongs to the AIMMGM. I have NO idea what the distribution of this may be outside of Mexico...the politics of its production (US based editor, Mexico theme!) have been complex and ugly.

For more focused information...there is the series of state Geological and Mining Monographs put out by the CRM (COREMI...predecessor of the SGM) during the 1990s. These large-format volumes cover most of the major mining states in Mexico and include not only descriptions of the geology of each mining district...with maps showing location of the individual mines...but also state-wide maps showing locations of hundreds of major and minor "mines" with an indication of what they have produced. This is on a geological map base with major roads and towns so they are easy to follow. A number of states paid to have their volumes translated into English...Chihuahua, Sonora, Guanajuato and San Luis Potosi, Sinaloa, Jalisco and Coahuila...for mining promotional purposes. As far as I know the series is out of print, but the state maps (revised with corrections made) can be down-loaded from the SGM website on a state by state basis.

There is also a huge amount of information on many of the major districts in the scientific and technical literature. We keep track of this and have generated a computerized bibliography (MEXBIB 3.5) with over 40,000 references. This allows rapid generation of a full bibliography for an area of interest that at least lets you know what to look for, if not where to find copies. Older literature on Mexico can be very scattered and hard to find, with libraries typically having broken sets of several different journals. (This is why my office is dominated by filing cabinets full of data). You can see examples of MEXBIB generated bibliographies in many of the Mineralogical Record articles on major Mexican mining districts...like Ojuela.

There are of course older volumes devoted to the minerals and mineralogy of Mexico (Panzcner, Johnson, Insituto Bulletins 40 and 41) that are of variable reliability and utility.

[javmex2]

Thanks Peter.