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Petrogenetic significance of trace elements in igneous quartz

Petrogenetic significance of trace elements in igneous quartz. Rune B. Larsen Francois Jacamon Bjorn Eske Sorensen Norwegian University of Science and Technology. Trace elements in quartz High T-P granites Medium T granites Low T granitic pegmatites Hydrothermal systems.

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Petrogenetic significance of trace elements in igneous quartz

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  1. Petrogenetic significance of trace elements in igneous quartz Rune B. Larsen Francois Jacamon Bjorn Eske Sorensen Norwegian University of Science and Technology • Trace elements in quartz • High T-P granites • Medium T granites • Low T granitic pegmatites • Hydrothermal systems Vintermøte 2006, Stavanger

  2. Why and how study trace elements in igneous quartz ? • Common mineral in allgranitic igneous systems • Normally present throughout the igneous evolution • Remarkably resistent to subsolidus alteration • Fingerprinting origin, igneous evolution and hydrothermal overprinting • Potential geothermometer • Economic applications, HPQ, future SoG-Si rawmaterials • LA-HR-ICP-MS or EMPA

  3. Quartz in dry granitic melts, high T, high P T: 850 falling to 625 C P: 7 to 5 kb

  4. 850 oC 640 oC

  5. Quartz in wet granitic melts, medium T low P

  6. Pegmatitic melts, low T, low P, wet and weird !

  7. Primary Qz Early Secondary Qz Late Secondary Qz

  8. During the igneous evolution of granitic melts Ti in quartz is falling whereas Ge in quartz is going up. There are exceptions to this principles, however, the Ge/Ti ratio is strongly temperarure dependent. Peraluminous granites, form qz with high Al contents. Evolved metaluminous granitic qz is low in this element. Alkaline granite comprise quartz with high K concentrations. Largely, the quartz composition is buffered by the melt composition i.e is sensitive to melt origin, fractional crystallization, events of replenishment and the exsolution of an aqueous phase. When infiltrated by aqueous fluids, Li, B, Al, Na, (K) and Fe are always remobilised whereas Ti, Ge and P normally are immobile. However, if inflitrated by high salinity alkaline fluids Ti, Ge and P are also mobilised Qz is very robust during subsolidus weathering and may largely preserve the igneous fingerprint where other major minerals are decomposed. Accordingly, qz partially preserve the igneous history and distinguish magmatic events in complex igneous terrains Granitic pegmatite, particularly metaluminous and hydrothermally infiltrated GP’s are promising targets for HPQ prospecting

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