Amphiboles of the Rare Earth Element-Rich Baerzhe Peralkaline Granite, Northeast China: Recorders of Fluoride-Silicate Melt Immiscibility and Rare Metal Enrichment
Bibliographic record
Abstract
Abstract Fluoride-silicate melt immiscibility has been proposed as an important control on light rare earth element (LREE) and Y enrichment in a peralkaline granite (e.g., the Strange Lake pluton in Canada). It remains uncertain, however, whether this immiscibility is a requirement for ore formation in mineralized peralkaline granites globally. In this contribution, we present an integrated mineralogical and chemical study of the REE-Zr-Nb-Be–mineralized Baerzhe peralkaline granite pluton, northeast China. We focus on the mineralogy and chemistry of amphibole and the bulk-rock geochemistry to investigate whether the metal enrichment at Baerzhe was facilitated by fluoride-silicate melt immiscibility or simply resulted from fractional crystallization. The Baerzhe pluton comprises, from early to late, a fine-grained hypersolvus granite, a porphyritic hypersolvus granite, and a transsolvus granite that evolved to pegmatite and a comb-textured amphibole unit. Hypersolvus granite enclave(s) can also be found within the transsolvus granite. The amphibole in these granitic units is arfvedsonite, providing evidence of fractional crystallization, magma mingling, fluoride melt immiscibility, fluid exsolution, and degassing. The presence of fluoride melt inclusions in arfvedsonite indicates that fluoride-silicate melt immiscibility took place in all units of the pluton except for the transsolvus granite, where rare metal mineralization occurs, and in pegmatite. The immiscibility was particularly intense in the porphyritic hypersolvus granite but very weak in other rock units, as evidenced by the abundance of fluoride melt inclusions in the former and lack of them in the latter. Most fluoride melt inclusions are rich in Ca and are enriched in LREEs, middle REEs (MREEs), and Y relative to heavy REEs (HREEs). The estimated volume of fluoride melt in the porphyritic hypersolvus granite was less than 1 wt %, storing about 2 to 6 wt % LREEs and up to 8 to 15 wt % MREEs and Y. The exsolution of fluoride melt, however, does not appear to have affected the trends of increasing concentrations of REEs and high field strength elements (HFSEs) in the coexisting silicate melt, which were driven by intense fractional crystallization of alkali feldspar, quartz, and arfvedsonite. Furthermore, the absence of fluoride melt inclusions in the transsolvus granite and pegmatite, together with their scarcity in the comb arfvedsonite unit, suggests that the early formed immiscible fluoride melt did not accumulate in the residual silicate melt. Fluoride melts appear to have played a limited role in the concentration of LREEs and Y to form the Baerzhe deposit. Instead, fractional crystallization of silicate minerals exerted a dominant control on the enrichment of REEs and HFSEs by factors of five to 20.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.006 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".