Discussions

💬 Home 🔎 Search 📅 Latest

╳Discussions

💬 Home 🔎 Search 📅 Latest

Groups

Recent Images in Discussions

PhotosArsenopyrite - Rod 2 mine, Snow Lake District, Manitoba, Canada

27th Mar 2015 17:31 UTCRichard Gunter Expert

A question for the experts out there on sulphosalt melting. I have several samples of sulphosalt melting where one phase is massive; in this case Chalcopyrite; in my Lengenbach sample it is Realgar and in my Chisel Mine sample it is Jordanite. Within the massive material are euhedral crystals of Arsenopyrite, Sartorite and Galena respectively. If the two phase melt is in equilibrium why would one phase be euhedral and the other is not?

27th Mar 2015 17:56 UTCRob Woodside 🌟 Manager

I would think that the euhedral xls formed while there was still room in the fluid.

27th Mar 2015 18:02 UTCDavid Von Bargen Manager

Are you sure that they formed from a melt? A lot of sulfides/sulfosalts are deposited from hydrothermal solutions.

Legenbach is a metamorphosed deposit so there is a good chance that the crystals grew in a solid medium (like garnet or staurolite crystals in schists).

27th Mar 2015 18:19 UTCRob Woodside 🌟 Manager

The vugs at Lengenbach were fairly isolated and presumably as the temperature fell and things xllized, elements in the vug were removed to crystals in the fixed ratios for that species. As the xllization depleted some elements, new and different species would add on to existing xls in epitaxi, further complicating any attempts at visual identification. I think this happened from a fluid state as most of these vugs are still open, unlike garnets in schist. However for species enclosed in dolomite, like tourmaline, etc, they may well have grown like garnets in a schist.

27th Mar 2015 18:19 UTCRichard Gunter Expert

Hi David:

All three of my examples have been noted as sulphosalt melts by Tomkins et al (2007): On the Initiation of Metamorphic Sulfide Anatexis, Journal of Petrology, v. 48 no.3 and other references therein. Tomkins has an interesting diagram where he has a Sartorite-Orpiment field (Sartorite usually occurs with Realgar) that has a maximum temperature of 300 C. This is well below the recorded melting temperature at Lengenbach of 500 C so the sample may be a retrograde melt at lower temperature than the peak.

Hi Rob:

If you use the analogue of a crystallizing melt in a layered silicate complex you do not have one phase (opx for example) crystallizing out in a fine grained second phase (anorthite in this case). All of the layered complexes I have seen have both cumulate phases being approximately the same grain size. The physics of a sulphosalt melt may be different than a silicate melt. I don't know if anyone has measured.

27th Mar 2015 18:31 UTCRichard Gunter Expert

Hi Rob:

Your second note came in while I was composing. Part of the problem at Lengenbach is that you have both melt and hydrothermal processes ongoing. In their Min Record article on Lengenbach Roth et al. (2014) have defined two separate sequences. The melt filled fractures, generally Realgar dominant, they call "Picassos". These are different than the hydrothermal vug filling with sulphosalt crystals. The Sartorite on this sample has been XRD identified so it is tied down. It puts a very tight temperature range on the melt as Sartorite converts to Baumhauerite at 300C. There are interesting melt-filled fractures on the sample where Sartorite filling converts to Realgar filling at a knife edge.

27th Mar 2015 19:11 UTCReiner Mielke Expert

Back to your original question. Basically " Materials with small heats of fusion have a nonfaceted (anhedral) morphology, and materials with large heats of fusion have faceted (euhedral) morphologies". http://www.minsocam.org/ammin/am60/am60_798.pdf So it is a function of the differences in the minerals being considered.

27th Mar 2015 20:09 UTCRichard Gunter Expert

Hi Reiner:

Thanks for the paper. I will have a look at it. There are many geological examples, with sulphosalt melts being the most recently investigated.

28th Mar 2015 00:01 UTCRob Woodside 🌟 Manager

I find that paper a little confusing and wonder what their cellular morphology is?

"Cellular morphologies are those which exhibit periodic structures,

usually considered to be due to diffusion of heat or matter.

Cood examples are skeletal crystals and dendrites. Spherulites may

also be cellular structures, and will be considered so here."

I would have thought that the surface energy would determine whether the xl was euhedral or anhedral. The higher the surface tension the more spherical the growth, reducing the surface energy. Fast growing skeletons or dendrites must have very low surface energies to produce so much surface area in such a short time.

Richard, Thanks I've been meaning to read that Lengenbach article.

28th Mar 2015 22:38 UTCRichard Gunter Expert

Hi Rob:

Roth et al have very little to say about Sartorite from Lengenbach. considering it is one of the major sulphosalts, especially in the old quarry, There is still a lot that is unknown about Sartorite. The sample itself was collected in 1959, well before there was any thought of sulphosalt melting so I wonder how many of the 1950's Lengenbach Sartorite samples have melt textures. The Chisel Mine and Rod Mine samples were collected before the sulphosalt melting theory was widespread and they also contain textures that could not be understood until long after the samples were taken.

Mindat.org is an outreach project of the Hudson Institute of Mineralogy, a 501(c)(3) not-for-profit organization.
Copyright © mindat.org and the Hudson Institute of Mineralogy 1993-2024, except where stated. Most political location boundaries are © OpenStreetMap contributors. Mindat.org relies on the contributions of thousands of members and supporters. Founded in 2000 by Jolyon Ralph.
Privacy Policy - Terms & Conditions - Contact Us / DMCA issues - Report a bug/vulnerability Current server date and time: May 14, 2024 15:30:46

Go to top of page