On the link between granites and pegmatites: the case study of the Li-rich mineralization from Castillejo de Dos Casas (Salamanca, Spain)
Bibliographic record
Abstract
<p>In the Castillejo de Dos Casas area (C2C) (Central Iberian Zone) different granitic (Villar de Ciervo granite) and pegmatitic units of Variscan age occur intruded into the Neoproterozoic-Cambrian metasediments of the Schist Greywacke Complex (SGC). These units include: (1) biotite-rich porphyritic granite; (2) two-mica granite; (3) muscovite ± tourmaline ± phosphates-rich, leucogranites; (4) barren to Li-rich aplite-pegmatite cupola; and, (5) Li-rich aplite-pegmatite dykes. Except (1), all these units are highly peraluminous (A/CNK in the range of 1.18-2.23), Ca-poor (0.09-0.87 wt% CaO), and P-rich (0.29-3.11 wt% P<sub>2</sub>O<sub>5</sub>). Units (4) and (5) are heterogeneous, showing different mineral associations. The most common consists of a fine-grained matrix of quartz, plagioclase and Li-mica, where coarser feldspar crystals grow perpendicularly to the contacts, and topaz, montebrasite, Fe-Mn-phosphates, petalite, elbaite, cassiterite and Nb-Ta oxides are accessory. A layered texture is also locally observed.</p><p>The origin of pegmatitic melts is somehow controversial. For decades they have been considered the residual portions originated by the fractional crystallization of granitic magmas (e.g. London, 2008). However, lately the anatectic model, which proposes that pegmatitic melts originate directly by low degrees of partial melting, is gaining more followers among pegmatite researchers (e.g. Simmons et al., 2016).</p><p>In the case of C2C, the aplite-pegmatite cupola is located over the two-mica granite and close to the leucogranitic units, whereas the aplite-pegmatite dykes intrude concordantly into the SGC materials, over and close to the granitic/pegmatitic cupola. These spatial relationships strongly suggest the existence of a petrogenetic link between granitic and pegmatitic units. Whole-rock data show a gradual decrease in the Ca, Fe, Mg, Ti, Ba, Y and REE contents and K/Rb ratio with fractionation, from units (1) to (5), parallel to an increase in Al, Mn, P, Li, F, Rb, Cs, Sn, Nb and Ta. Similarly, chemical composition of main mineral phases shows gradual changes from the less evolved unit (1) to the most fractionated one (5). A continuum is observed for micas, with a progressive Li, F, Rb and Cs increase, parallel to a K/Rb decrease. Alkali feldspars show a gradual decrease of the K/Rb ratio for K-feldspar and of Ca for plagioclase; whereas tourmaline becomes Li-richer and Fe-poorer from (3) to (5) (it has not been identified in units (1) and (2)). Therefore, taking into account the spatial relationships of the 5 units, as well as their chemistry at whole-rock and mineral scales, the most feasible origin for the pegmatitic melts in the C2C area corresponds to the fractionation of a parental granitic melt that well could correspond to the unit (1) of the Villar de Ciervo granite, and that would evolve through the units (2), (3) and (4), up to the most fractionated unit (5) of the Li-rich aplite-pegmatite dykes.</p><p> </p><p>London, D., 2008. Pegmatites. Canadian Mineralogist, Special Publication n° 10, pp. 347.</p><p> </p><p>Simmons, W., Falster, A., Webber, K., Roda-Robles, E., Boudreaux, A., Grassi, L.R., Freeman, G., (2016): Bulk composition of Mt. Mica pegmatite, Maine, USA: implications for the origin of an LCT type pegmatite by anatexis. Can. Mineral. 54, 1053-1070.</p>
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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 | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 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".