Ecandrewsite (ZnTiO3), the zincian end-member of the ilmenite group minerals (IGM) has been found as an accessory relic phase in amphibolites from the Upper Proterozoic-Lower Cambrian metamorphic basement of the Pampa de Olaen region, in the eastern hillside of the Sierra Grande, Córdoba, Argentina. IGM grains occur as anhedral to subhedral inclusions as centers of coronitic titanite, as a result of retrograde metamorphic reactions. Electron microprobe analyses of IGM reveal compositions between Ec56Pph23Ilm21 and Ilm95Pph5 along a solid solution trend ranging from manganoan ferroan ecandrewsite toward ilmenite s.s., passing through intermediate members such as ferroan manganoan ecandrewsite, zincian manganoan ilmenite and manganoan ilmenite. Ecandrewsite and other members of the IGM are considered refractory accessory minerals of a basic igneous rock (likely basalt) later on affected by medium grade regional metamorphism. The inclusions of IGM in titanite would represent non-consumed remnants of the protholithic IGM after coupled reactions with plagioclase that led to the formation of titanite during a retrograde metamorphic event. Even considering that Zn is a relatively widespread element in the metasedimentary associated sequence, we believe that the chemical trend between near end-members ecandrewsite and ilmenite reflects the magmatic composition of IGM in the protholith, where the variations of the Zn contents were controlled by the substitution of Fe by Zn+Mn in the absence any type of regular zonation. However, it is not discarded that chemical adjustments among members of the IGM could have been introduced during prograde regional metamorphism. This would be the first worldwide record of ecandrewsite in amphibolites.
I find your work very interesting, but unfortunately I cannot download the video presentation. Probably, there is a problem wiht the link. Pleaee, could you provide a video or a simple PowerPoint presentation?
In the meanwhile, I would like to ask you some questions:
Did you find gahnite or kreittonite?
Is the amphibole rich in Zn?
Did you find sulfides or barite?
The absence of suflides could explain the formation Zn-rich oxides and silicates. Thus, in a paper by Chukanov et al. (2020; Mineralogy and Petrology volume 114, pages129–140), it is reported unusually Zr-rich amphiboles (up to 23 wt% ZnO). This amphibole also contains relativley high Cu. These authors explain the high content of chalcophile elements in amphibole becasue of the absence of sulfides, bieng sulfur immobilised by the formation of barite.
Best regards
José Francisco Molina
How are you? First of all, we are grateful for your interest on this abstract. I do not know why the video can not be opened, perhaps there is a problem with the page, I will ask to the Conference Secretary if they can fix this. Meanwhile, I send you the Drive link where the video have been uploaded:
https://drive.google.com/drive/folders/1NLT3U_yodkSF96o35FbomGdy61j1IgAa?usp=sharing
Did you find gahnite or kreittonite? No, we did not find any of those species. But around the amphibolite outcrop (1 km), we found another mineral from the spinel group, but in a skarn, not in amphibolite. A paper referred to this species is uploaded in ResearchGate (https://www.researchgate.net/publication/335128465_ZINCOCROMITA_EN_UN_SKARN_DEL_GRUPO_MINERO_LOS_GUINDOS_CORDOBA_PRIMER_REGISTRO_EN_ARGENTINA)
Is the amphibole rich in Zn? We are still in process to do a few whole rock analyses on amphibolites of the mining district to check their trace element content includying Zn; this study is in progress.
Did you find sulfides or barite? We didn't find baryte, but there is chalcopyrite disseminated in the amphibolite, partially replaced by covellite as a few 5 µm anhedral grains included in titanite and plagioclase. The amphibolite outcrop is near a shear zone where ultramafic and orthoamphibolites were reported, but there isn´t any study about the protholithic ortho- or para-metamorphic origin of this amphibolite, so the final comprehension of the origin of ecandrewsite in these rocks is still underway.
The absence of suflides could explain the formation Zn-rich oxides and silicates. Thus, in a paper by Chukanov et al. (2020; Mineralogy and Petrology volume 114, pages129–140), it is reported unusually Zr-rich amphiboles (up to 23 wt% ZnO). This amphibole also contains relativley high Cu. These authors explain the high content of chalcophile elements in amphibole becasue of the absence of sulfides, bieng sulfur immobilised by the formation of barite.
Spectacular information!! I see that the work of Chukanov and collaborators is recent (2020); we missed it at the time of sending the abstract! We acknowledge your data that for sure will help us a lot.
Thanks, again, for all your interest, help and data information!
thank you very much for your answer
Un saludo
José
