TÁMOP-4.2.1/B-09/1/KMR-2010-0003

Enargite from the Lahóca high-sulphidationepithermal gold deposit, Recsk (Hungary): joint application of infrared microscopy –

microthermometry and orientation imaging microscopy

Ágnes Takács & Ferenc MolnárDepartment of Mineralogy, Eötvös Loránd University

ECROFI-XXIMontanuniversität Leoben, Austria

9-11. August, 2011.

Research topic

50 mμ

IR microscopic picture of enargite• Geological background of the studied area

• IR transmittance of opaque minerals

• IR Microscopy – VIS/IR fluid inclusion microthermometry

• Orientation Imaging Microscopy (OIM)

• VIS/IR Micro-Spectrophotometry

• Results of OIM and IR transparency

• Results of fluid inclusion microthermometry

• Summary

-Reconstruction of the ore forming fluid flow system at the Lahóca Cu-Au deposit (NE-Hungary)

Contents

Ore microscopic picture ofenargite and luzonite (+N)

- Infrared transmittance of opaque minerals in the connection to the crystal’s orientation

Lahóca Hill, Recsk

Geological background of studied area

Ore microscopic picture of enargite andluzonite (+N)

High sulphidation type Cu-Au deposit at Lahóca Hill, (Resck) NE Hungary

IR transmittance of opaque minerals

• The IR radiation has lower energy (longer wavelength) than visible light, thus the light is not absorbed by the opaque minerals. (Shuey, 1975)

20 μmIR microscopicpicture of stibnite

Theoretical background

List about the band gap energies of some opaque minerals (after Shuey, 1975 and

Campbell et al., 1984)

IR Microscopy – VIS/IR Fluid InclusionMicrothermometry

The figure shows the applied IR system, which optimalized for transmitting IR radiation.

•fluid inclusion petrography and microthermometry on quartz werecarried out using: - Olympus BX51 microscope with IR and other light filter

- Linkam FTIR 600 type stage with glass windows

• IR fluid inclusion petrography and microthermometry onenargite were performed using:

- Olympus BX51 microscope without any light filter- Olympus MIR Plan objectives- Linkam FTIR 600 type stage with sapphire windows- Hamamatsu C2400 IR sensitive camera

The camera’s maximum observable wavelength: ~2400 nm

• The reproducibility of the measurements was ±1°C both on high temperatures and below 0°C.

enargite-hosted fluid inclusions

Technical background

IR Fluid Inclusion Microthermometry

Homogenization temperature Final ice melting temperature

Enargite-hosted two phase (L+V) fluid inclusion

The calibration measurements to avoid and eliminate the IR radiation caused problems described byMoritz (2006)

There are no significant differences between the temperatures of the phase changes at various light intensity

Infrared Microscopy

IR microscopic pictures of enargite crystals

• growth banding • patchy transparency

. . . but we couldn’t explain the patchy transparency with these effects

• The thickness of the sample and differences in the chemical composition (for example replacement of As by Sb in the structure) may influence the IR transmittance

•optical properties of minerals are influenced by the orientation of the crystal, hence we investigated the IR transmittance in the connection to the crystals’ orientation of enargite.

Variable transmittance of enargite under IR microscope

Orientation Imaging Microscopy (OIM)

• crystallographic orientation of single and polyphase crystalline materials based on the electron backscatter diffraction (EBSD) patterns in the scanning electron microscope (SEM)

Crystallographic orientation data were collected atthe Eötvös Loránd University (Budapest) using

EBSD patterns (Kikuchi patterns) ofenargite and luzonite crystals

• FEI Quanta 3D FIB-SEM withHikari EBSD detector

• with accelerating voltage of 20 kV and beam current of ~5 nA

• angular resolution is ~1° with a spatial resolution of ~50 nm

• EBSD data were processed usingthe EDAX-TSL software package

Sample/SEM reference system

Schematic illustration about the formation of Kikuchi lines and setting of the measurements

VIS/IR Micro – Spectrophotometry

•Quantify the transmitted light in the infrared light range

•Visible light range (~400-700 nm)

• Infrared light range (~800-1800 nm)

Reference data for enargite and luzoniteafter Criddle&Stanley (1993)

- transmitted light: directly measuring the transmitting light to define the optical indicatrix in the IR light range

- reflected light: distinguish the two mineral species

Results of OIM and IR transparency

IRTransp.sample

Crystal Orientation maps200 µm

IR microscopic picture

IR Opaquesample

TD

RD

Pole figure

Pole figure

Inversepole figure

Inversepole figure

IR microscopic

picture

Phase map

A

B

C

A

B

C

Coloured inverse pole figures and map

Luzonite

EnargitePole figure of enargite

Results of OIM and IR transparency

IR Transparent

200 µm

IR Opaque

• thickness of the samples: ~100 µm

IR transmittance spectrums of IR transparent and IR opaque enargite

Results of OIM and IR transparency

Summary of IR transparency and OIM

Pole figure Inverse pole figure

• there are connection between the enargite crystal’s orientation and IR transparency

• 10% transmittance in the IR light range enough for fluid inclusion measurements with the sample thickness of ~ 100 µm

Results of fluid inclusion microthermometry

Early quartz • primary fluid inclusions• mostly two phase (L+V)• sometimes contain trapped solid phase• homogenizationtemperature range: 250-300°C

Enargite

• primary fluid inclusions• two phase (L+V)• the homogenizatontemperature range:170-230°C

Early quartz

SE

NNW

Late quartzEnargite

NaCl-H2O

Summary

• Application of up to date techniques eliminate the previously described problems with infrared microthermometry in opaque minerals

Necked-down secondary fluid inclusions in enargite

•There are connection between the enargitecrystal’s orientation and IR transparency

• The ore forming stage of the Lahóca Cu-Audeposit took place in the temperature range of 170-230°C

• The decreasing temperature and increasing salinity (from ~1 to ~8 NaCl equiv. wt.%) of the ore forming stage shows spatial change from the NNW part to the SE part of the deposit

• The enargite crystal’s fluid inclusions preserved such stages of the ore forming processes in the Lahóca deposit, which otherwise could not be reconstructed on the basis of conventional studies of fluid inclusions in transparent minerals

The European Union and the European Social Fund have provided financial support to the project under the grant agreement no.TÁMOP 4.2.1./B-09/KMR-2010-0003.

Thank you for your attention!

We are grateful to Istvány Dódony for his useful comments and to Zoltán Dankházi for his help in the EBSD measurements.

Acknowledgment