Petrogenetic significance of trace elements in igneous quartz

Rune B. LarsenFrancois JacamonBjorn Eske SorensenNorwegian 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

Why and how study trace elements in igneous quartz ?

Common mineral in all granitic 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

Quartz in dry granitic melts, high T, high P

T: 850 falling to 625 C

P: 7 to 5 kb

850 oC

640 oC

Quartz in wet granitic melts, medium T low P

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

Primary Qz

Early Secondary Qz

Late Secondary Qz

0.1

10

11

00

10

00

0 . 1 1 1 0 1 0 0

E r z g e b ir g e , G r a n i t e ( 4 )

K le iv a n G r a n i t e

K r u s n é H o r y , G r a n i t e ( 3 )

K r u s n é H o r y

G r a n i t i c P e g m a t i t e ( 3 )

I - T y p e G r a n i t e

M e t a l u m i n o u s

S o r A - T y p e G r a n i t e

P e r a l u m i n o u s

W o r l d I g n e o u s Q u a r t z

N = 5 1 7

1) Jung L 2) Watt RG, Wright P, Galloway S. & McLean C 3) Müller A, Kronz A & Brieter K 4) Müller A, Weidenbeck M, van den Kerkhof A, Kronz A & Simon K

(1992)(1997)

(2002)(2002)

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