Abstract Details
(2020) Barite Study Constrains the Origin of the Mountain Pass Carbonatite REE Deposit and Links to Alkaline Magmatism, California, USA
Watts K & Haxel G
https://doi.org/10.46427/gold2020.2825
The author has not provided any additional details.
03i: Room 1, Thursday 25th June 22:12 - 22:15
Kathryn Watts
View abstracts at 4 conferences in series
Gordon Haxel View abstracts at 2 conferences in series
Gordon Haxel View abstracts at 2 conferences in series
Listed below are questions that have been submitted by the community that the author will try and cover in their presentation. To submit a question, ensure you are signed in to the website. Authors or session conveners approve questions before they are displayed here.
Submitted by Anthony Lanati on Thursday 25th June 13:39
Thanks for a really interesting presentation. I was wondering where you mention the secondary enrichment of REE's by the Sr rich fluid, could you elaborate or speculate on what the composition of the fluid work be? For context, I was wondering if you could apply some of the same methods igneous petrologists working with mantle melts use to back calculate a fluid composition by undertaking a mass balance style approach to the composition of the primary and secondary mineral phases. As you can imagine these do not provide an empirical composition, but perhaps it would give you an indication.
Great question, and one I will be trying to untangle with future work. At this point, what I can say is that both the Sr-rich and REE-rich fluids came in later than the primary barite crystallization, based on Sr alteration/replacement of barite rims and REE carbonate phases (bastnasite, sahamalite) along Sr-enriched barite margins or in cross-cutting veins. These could be different fluid pulses for the Sr and then REE chemical overprint, or they may be part of the same fluid pulse. More textural and chemical (including isotopic) data are needed to resolve this question, and then mass-balance calculations as you suggest could be very informative. Thanks for the suggestion.
Thanks for a really interesting presentation. I was wondering where you mention the secondary enrichment of REE's by the Sr rich fluid, could you elaborate or speculate on what the composition of the fluid work be? For context, I was wondering if you could apply some of the same methods igneous petrologists working with mantle melts use to back calculate a fluid composition by undertaking a mass balance style approach to the composition of the primary and secondary mineral phases. As you can imagine these do not provide an empirical composition, but perhaps it would give you an indication.
Great question, and one I will be trying to untangle with future work. At this point, what I can say is that both the Sr-rich and REE-rich fluids came in later than the primary barite crystallization, based on Sr alteration/replacement of barite rims and REE carbonate phases (bastnasite, sahamalite) along Sr-enriched barite margins or in cross-cutting veins. These could be different fluid pulses for the Sr and then REE chemical overprint, or they may be part of the same fluid pulse. More textural and chemical (including isotopic) data are needed to resolve this question, and then mass-balance calculations as you suggest could be very informative. Thanks for the suggestion.
Submitted by Kathryn Goodenough on Thursday 25th June 15:01
Thanks for the presentation Kathryn, really interesting. Do you think the barite is all magmatic in the syenite-shonkinite suite, or do you think some of it could be related to later-stage metasomatism (potentially carbonatite related)? What do you think is the genetic relationship between the syenitic rocks and the carbonatite? I am really struck by the mineralogical similarities between the Mountain Pass suite and some of the potassic, high Ba-Sr plutons we have worked on in NW Scotland.
Another great question, and one that requires further work. I have focused on what I interpret to be magmatic/primary barite in this presentation based on the current data and interpretations (e.g. association with primary phases), but I have observed some very small-scale veins of barite, and barite filling in cleavage planes of phlogopite in the syenite-shonkinite rocks that appears to be secondary. I need to analyze these features and look for other secondary textures to evaluate the similarity or dissimilarity to what is currently interpreted as primary barite. The syenite, shonkinite, and carbonatite magmatism at Mountain Pass was long-lived (10s Myr) based on our geochronology data. My working interpretation is that they represent a series of partial melts of variably metasomatized mantle, from a common, but heterogeneous source. Crustal assimilation also appears to be important based on isotopic data and inherited crustal zircons. I would certainly like to hear more about your NW Scotland examples!
Thanks for the presentation Kathryn, really interesting. Do you think the barite is all magmatic in the syenite-shonkinite suite, or do you think some of it could be related to later-stage metasomatism (potentially carbonatite related)? What do you think is the genetic relationship between the syenitic rocks and the carbonatite? I am really struck by the mineralogical similarities between the Mountain Pass suite and some of the potassic, high Ba-Sr plutons we have worked on in NW Scotland.
Another great question, and one that requires further work. I have focused on what I interpret to be magmatic/primary barite in this presentation based on the current data and interpretations (e.g. association with primary phases), but I have observed some very small-scale veins of barite, and barite filling in cleavage planes of phlogopite in the syenite-shonkinite rocks that appears to be secondary. I need to analyze these features and look for other secondary textures to evaluate the similarity or dissimilarity to what is currently interpreted as primary barite. The syenite, shonkinite, and carbonatite magmatism at Mountain Pass was long-lived (10s Myr) based on our geochronology data. My working interpretation is that they represent a series of partial melts of variably metasomatized mantle, from a common, but heterogeneous source. Crustal assimilation also appears to be important based on isotopic data and inherited crustal zircons. I would certainly like to hear more about your NW Scotland examples!
Submitted by Sam Broom-Fendley on Thursday 25th June 20:22
Thanks Kathryn, I enjoyed your presentation, and look forward to hearing more about Mountain Pass in the future. I've never been entirely convinced by the idea that REE mineralisation at Mountain Pass is a magmatic process, and your data look like they also, tentatively, support a later crystallisation stage. Similar to the question you asked me - do you intend to undertake any thermometry in the future? I wonder what could be done, or if anyone has tried thermometry between barite and celestine? Are there any fluid (or melt?) inclusions in your barite samples?
Ha, excellent question Sam, and yes, as you might imagine from mine to you, this is something I am very interested in pursuing. As there are many pulses of primary and secondary processes apparent in the thin sections, this will be difficult, but necessary to constrain magmatic to hydrothermal growth. Possibly O isotope thermometry of carbonate and other coexisting phases. This is something I need to think more about and get a better handle on what is possible based on the (complex) mineralogy of the samples.
Thanks Kathryn, I enjoyed your presentation, and look forward to hearing more about Mountain Pass in the future. I've never been entirely convinced by the idea that REE mineralisation at Mountain Pass is a magmatic process, and your data look like they also, tentatively, support a later crystallisation stage. Similar to the question you asked me - do you intend to undertake any thermometry in the future? I wonder what could be done, or if anyone has tried thermometry between barite and celestine? Are there any fluid (or melt?) inclusions in your barite samples?
Ha, excellent question Sam, and yes, as you might imagine from mine to you, this is something I am very interested in pursuing. As there are many pulses of primary and secondary processes apparent in the thin sections, this will be difficult, but necessary to constrain magmatic to hydrothermal growth. Possibly O isotope thermometry of carbonate and other coexisting phases. This is something I need to think more about and get a better handle on what is possible based on the (complex) mineralogy of the samples.
Submitted by Sam Broom-Fendley on Thursday 25th June 20:22
Thanks Kathryn, I enjoyed your presentation, and look forward to hearing more about Mountain Pass in the future. I've never been entirely convinced by the idea that REE mineralisation at Mountain Pass is a magmatic process, and your data look like they also, tentatively, support a later crystallisation stage. Similar to the question you asked me - do you intend to undertake any thermometry in the future? I wonder what could be done, or if anyone has tried thermometry between barite and celestine? Are there any fluid (or melt?) inclusions in your barite samples?
Thanks Kathryn, I enjoyed your presentation, and look forward to hearing more about Mountain Pass in the future. I've never been entirely convinced by the idea that REE mineralisation at Mountain Pass is a magmatic process, and your data look like they also, tentatively, support a later crystallisation stage. Similar to the question you asked me - do you intend to undertake any thermometry in the future? I wonder what could be done, or if anyone has tried thermometry between barite and celestine? Are there any fluid (or melt?) inclusions in your barite samples?
Submitted by Sam Broom-Fendley on Thursday 25th June 20:54
Thanks Kathryn, I enjoyed your presentation, and look forward to hearing more about Mountain Pass in the future. I've never been entirely convinced by the idea that REE mineralisation at Mountain Pass is a magmatic process, and your data look like they also, tentatively, support a later crystallisation stage. Similar to the question you asked me - do you intend to undertake any thermometry in the future? I wonder what could be done, or if anyone has tried thermometry between barite and celestine? Are there any fluid (or melt?) inclusions in your barite samples?
Thanks Kathryn, I enjoyed your presentation, and look forward to hearing more about Mountain Pass in the future. I've never been entirely convinced by the idea that REE mineralisation at Mountain Pass is a magmatic process, and your data look like they also, tentatively, support a later crystallisation stage. Similar to the question you asked me - do you intend to undertake any thermometry in the future? I wonder what could be done, or if anyone has tried thermometry between barite and celestine? Are there any fluid (or melt?) inclusions in your barite samples?
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