Advanced intracontinental rifting

SEDEX deposits (stratiform)

MVT Pb-Zn deposits (stratabound)

1

2

1

2

(After Goodfellow et al., 1993)

100 kmThe Vares Fe-SEDEX deposit, Bosnia & Herzegovina

The Vares Fe-SEDEX deposit, Bosnia & Herzegovina

- closed

- 500 Mt of iron ore

The Vareš deposit, geological cross-section

Massive pyrite bodyOre bodies

A. Massive pyrite

B. Barite

C. Siderite

D. Hematite + cherts

Barite

Siderite beds

Hematite + cherts

Pyrite and siderite bodies Limestone with ammonites

Ammonite

Hematite and chert beds

The carbonate part of peperite contains Triassic index conodont fauna:

Paragondollela excelsa, Paragondollela foliata foliate, Paragondollela foliate

inclinata, Nurella sp., CAI 6 ½ , what appropriates to the Langobardian (Upper

Ladinian).

The basalt was extruded into soft, unconsolidated sediments, of the Triassic

rifting basin, and there is still no evidences of the oceanic crust which developed

afterwards, possible in Jurassic time.

The Smreka basalt quarry

Basaltic lava + Seawater → Calcite + Siderite + Chlorite + Zeolites ± Epidote

Primary FIs:

Coexistence of liquid-rich and

vapour-rich FIs → Boiling effect !

Salinity ≈ 10 wt.% NaCl equ.

TH = 275 to 290°C

→ formation depth: 600 - 770 m

Secondary FIs:

Salinity = 3.5 – 5.7 wt.% NaCl equ.

TH = 60 to 110°C

→ modified seawater

600 - 770 m

Formation depth in the

seawater 600 – 770 m !

100 kmThe Idrija Hg deposit, Slovenia

The Idrija Hg deposit, Slovenia

- closed

- past production of 128,000 tons of Hg

- still contains 10% of the world’s known Hg reserves

A B

C

A Ore breccia cemented with cinnabar

B cinnabar-pyrite beds

C native mercury within organic-rich shale

Cinnabar (HgS)

(After Goodfellow et al., 1993)

Mississippi Valley-type (MVT)

Pb–Zn deposits

Ore characteristics

• Mineralization type: Epigenetic Pb-Zn sulphide deposits

• Host rocks: carbonates (usually dolostones)

• Gangue minerals: carbonates (pre-, syn- and post-ore), barite, fluorite

• By-products: Ag, Ge, Cd

• Geological setting: intracratonic basins or passive margins of rift basins

• Ore bodies: stratabound type (small- to medium-size irregular lenses and/or veins and breccia fillings)

• Ore textures: open-space fillings, colloform sulphides, late carbonate fillings,…

Ore-forming fluid characteristics

• Na-Ca-chloride rich brines

• Salinity: 10-30 wt.% NaCl equ. (usually around 25 wt.% NaCl equ.)

• Temperature: 60-160°C

• Presence of hydrocarbons

• Fluid flow is controlled by the host rock permeability

pH

Hydrothermal solubility of sphalerite

Depositional mechanism

• Neutralization of base-metal and H2S bearing fluids by carbonates• Cooling of ore-bearing fluids• Reduction of base-metal and (SO4)2- bearing fluids by organic matter/hydrocarbons

Mežica, Slovenija

• Tip mineralnog ležišta: Pb-Zn, Mississippy valley tip (Mežice-Bleiberg tip)

• Rudni minerali: sfalerit, galenit, markazit, pirit

• Jalovinski minerali: wulfenit, anglezit, ceruzit, kalcit, deskloazit, epsomit, grinokit, gips, hemimorfit, melanterit, smitsonit

• Stijena domaćin: ladinička serija Wetterstein karbonata i Raibl slojeva (šejlovi, onkoidi, bitumenozni dolomiti i kalkareniti)

• Tip rude: • 1) stratabound Pb-Zn ruda u obliku silova ili žica• 2) metasomatska Pb-Zn ruda

• Starost: Srednji Trijas; Karnik, 230 - 220 Ma

• Prvi zapisi o rudarenju s područja Mežice iz 1665. godine

• 19 Mt rude @ 5.3% Pb + 2.7% Zn

vulfenitna druza

Wulfenitna druza

Mežica danas

ih

Geološki profil kroz rudno tijelo Union