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