FMF - Friends of Minerals Forum, discussion and message board

[jorgedavid]

[quote="Tobi"]Wonderful specimens, thank you for sharin


Really nice . The next Tucson 2014 will be more clear the future of this new locality, still its not clear the ubication, Morelos, or Guerrero, or Mexico States. Any way, this locality have one more feature: green and complex habit of quartz.

[jorgedavid]

Now here is a green quartz spécimen associated with amethyst, amethyst crystal has a phantom green color also.
I said that the future of this locality we will see in tucson 2014 because some dealers will if arouses interest this localities there will be more demand for specimenes and have more people looking for the actual locality and may contact the miners to help them to dig and retain the best crystals . If in the state of Morelos no mining experience, if Guerrero also the mining experience is low and if in the state of Mexico, near the mining district Zacualpan only security issues we will have to take into account to contact miners directly

[jorgedavid]

Now we have a new locality for Amethyst in México, Tejupilco.

[Jean Sendero]

At the Tucson show 2015, we started to see some regular looking calcite reported to be from the Palmarejo mine in the state of Chihuahua. The two dealers that had some were asking an arm and a leg for some chipped scalenohedra, of grayish color and opaque. I ended up never acquiring one. Nevertheless, I had never heard of the mine so I did a little bit of investigating on the internet. Those findings are summarized below but in the course of doing this, I started to find and acquire several new calcite specimens which I believe, can compete with any great Mexican calcite locality by the diversity of crystal forms, the clarity of some crystals, the presence of spectacular inclusions and fantastic fluorescence. Color diversity is missing but compensated by transparency.

The mine is owned and operated by Coeur Mexicana and located on the western flank of the Sierra Madre Occidental, 270 km to the southwest of Chihuahua as the crow fly. The units forming the Sierra, poorly deformed and relatively flat-lying sequence of Tertiary-aged volcanic and sedimentary rocks, are cut by numerous intrusive rocks. The Sierra Madre hosts several ore deposits and the Palmarejo Mine is one of them.

The Palmarejo mine is harvesting Au and Ag from a complex system of veins, breccias and stockwork. It is classified as an epithermal low sulphidation system. The vein system trend generally northwest to southeast and dip either southwest or northeast. The dip on the structures ranges from about 45 to 70 degrees. In the mineralized portions of the structures, gold and silver are zoned from top to bottom with higher silver values occurring in the upper parts and higher gold values in the lower parts, sometimes accompanied by base metal mineralization, though variations are common.

The veins systems have a diversified mineralogy according the 43-101 metallurgy section which mentions 19 species of native elements and minerals or series hosting the Au and Ag. These are in no special order, electrum, native gold, native silver, jalpaite, aguilarite, pyrite, sphalerite, galena, chalcopyrite, altaite, billingsleyite, cervellite, tennantite-tetrahedrite, proustite, pearcite-polybasite, covellite-digenite, mckinstrite and stromeyerite. To date, and to my surprise, none of these have been reported, to my knowledge, as “quality collection specimen”.

The Palmarejo property contains a number of mineralized zones, the most important of these being the Palmarejo area where 5 zones or "clavos," are being exploited. La Prieta and La Blanca zones are exploited by open pit while the other three zones by underground mining. The open pit is exploited as usual with drill and blast, truck and shovel operations. The underground workings are accessed via three separate portals. The mine produce from all mining areas approximately 6,000 tonnes of ore per day. The ore is crushed, milled, and floated which results the recovery of silver and gold forming a doré shipped to Coeur’s smelting and refining partners in the U.S. and Europe.

Back to the calcite, the photos below are telling the story, for now. At least two generations of calcite are present, the latest one growing on top of the first one in in what seems to be on occasion, continuous without a real break other than the transitional deposition of what has been called Mn and Fe oxides.

The first episode of crystallization appears to be preferentially forming scalenohedron. Some nice twinned crystals and even some big fish tail looking ones, are present. This early phase of crystallization produces super clear to grayish to brownish colored scalenohedron crystals. Inclusions of reported Mn oxides are common and can have a beautiful arborescent form in the core of the crystal.

The second phase of crystallization covers the original scalenohedra crystals and produce some modified scalenohedra generally of clear nature to foggy. The second generation growth can partially or fully embed the first generation crystals. On occasion it is possible to observe a vertical growth on top of the pre-existing crystal suggesting continuity in the crystallization following a short hiatus that allowed the deposition of the Fe or Mn oxides.

The two generations of calcite are further defined by their distinctive fluorescence. The first generation under short wave is a spectacular bright orangey red, or with lesser intensity under medium or long wave exposition. The second generation does not fluoresce making for a bright core surrounded by non-fluorescent material.

The photos below show the diversity in crystal forms, examples of the two generations, the inclusions and the fluorescence. I hope you will agree with me that these are starting to stand out compared to the original find in late 2014. Note size of the crystals on some of the specimens, up to 15 cm.

It would be interesting to know from which workings these are coming from. If anyone knows, I would appreciate additional precision on the provenance.

The fluorescence of the calcite is likely due to the presence of Mn in the fluids, so why would the inclusions be Mn oxides if the system was oversaturated in Mn. Should we be expecting one of these days to see some rhodocrosite coming from Palmarejo?

Could some of the inclusions be something a little more exciting (i.e. sulfosalts instead of Fe or Mn oxides)? In the paragenetic sequence of these deposit type, it is not uncommon to have the sulphides and sulfosalts precipitated in between calcite and quartz stages.

Cheers

Jean

p.s. I Photoshopped some of the backgrounds to provide homogeneity. The minerals are untouched. Thank you to Moninaz123, Ricblair369 and Southershrike, all eBay vendors.

[Jordi Fabre]

Thanks Jean, new locality added and applied!

[Jean Sendero]

What’s new in Mexico……I just realized that it’s been one year since I posted something in this column. May be because we did not see many really new finds coming out of Mexico or now that I am based out of Santiago Chile, I am further remote and not as much in the loop. Tom Moore, in the Mineralogical Record following the Tucson Show, reported new digging activities at some classic localities: Los Lamentos, Milpillas and the mention of kobyashevite from Mapimí. But over the past 6 months, I, and others, came across some very interesting finds, although small, these are mineralogically significant for Mexican localities.

At the time of the Tucson show in late January-early February, El Potosi mine in the West Camp at Santa Eulalia delivered some pale green adamite mixed with botryoidal looking smithsonite. The adamite is spectacularly fluorescent. Really amazing fluorescence. I am aware of at least three dealers marketing this material.

[Jean Sendero]

It is not often that we see other minerals than chalcopyrite from the Bolivar mine in the Piedras Verde district. On occasion, it has yield some interesting specimens such as the cosalite find of late 2007, early 2008. The operation is currently mining the “El Gallo Superior” orebody and in April 2016, a small lot of approximately 25-30 specimens of datolite surfaced and are mainly miniature in size. Originally thought to be calcite, these were analyzed by Dr. Peter Megaw and confirmed to be datolite. The bladed disc shape morphology of the crystals is deceiving. Some specimens will have fine chalcopyrite dusted on top or as larger “chunks” at the back.

[Jean Sendero]

More recently in June 2016, the Ojuela Mine at Mapimí delivered the unexpected. Due to the lack of rains, the water is exceptionally low in the mine and the miners have been able to access the deeper levels. We have seen over the past year a very small lot of gemmy looking small legrandite and more cerussite of much better quality than the ones from 2014. The cerussite is often associated with remnants of sulphides such as massive galena. So in mid-June of this years, the miners, while working on pisos 13 or 14 (aka levels 6 and 7) below the legrandite find, encountered a small pocket of sulphides. Approximately 100 specimens were produced ranging in size from miniature to small cabinet. The specimens consists of either 1) gun powder grey, simple modified cubes or spinel twins crystals of galena with little to good luster, some with a fine dusting of white carbonate or protruding masses of fine native silver and/or silver wires and 2) more complex lustrous crystals with associated arsenopyrite and fluorite and 3) nice purple partially gemmy fluorite forming cubes and modified cubes on which the carbonate matrix or remnant of arsenopyrite resides. I am told that the lot was split amongst three dealers.

Happy hunting. I have seen specimens from these finds on the market with the exception of the datolite.

[Tobi]

[Jean Sendero]

Tobi,

these are very new and nothing equal to these had surfaced before. Morphology and mineral associations are different from what we have seen from the higher part of the Ojuela where secondary minerals prevailed. These are from the deeper areas. The fluorite are seen with either a dusting of the white carbonate or with arsenopyrite. The galena can have the moderate luster grey gun powder color with a dusting of the white carbonate or have a better luster. They are then associated with fluorite arsenopyrite and on occasion native silver. I suspect, these associations, morphology, luster etc... is dependent if the specimens are from the top or bottom of the pocket.

Hope that more will come out as long that access to piso 13-14 (level 6-7) remains above the water table.

J

[Jean Sendero]

The cross section of the mine will give everyone a general idea of the depth of the new galena-fluorite-arsenopyrite-silver find occurred.

[Turbo]

One of the more recent calcite twins from the Palmarejo Mine. Feb of last year was when I first began to see them at shows.

Ed Bayley

[Brent Lockhart]

Does anyone have information on the associated minerals seen with the recent batch of Legrandites from the Ojuela Mine?