Underground mining of U in northern

Bohemia

Vojtěch Vokál, Jiří Mužák

DIAMO, s. e., Stráž pod Ralskem, Czech Republic

Overview of U exploration and mining

activities in the Czech Republic 1946-2018

DIAMO, state enterprise, Stráž pod

Ralskem

Uranium exploration started in 1946

using geological, geochemical and

geophysical methods and drilling

technique.

Thousands of radiometric anomalies and

more than 15,000 uranium occurrences

were discovered by 1989. Evaluation of

186 uranium mineralized objects led to

mining at 86 uranium deposits.

Overview of U exploration and mining

activities in the Czech Republic 1946-2018

U mining technologies: underground mining, open pits and ISL.

Estimated total uranium production by 2018 > 132,000 t of U (metal).

Underground mining at the uranium deposits Hamr

and Břevniště, Czech Republic

Localization of the deposits

Děčín

Ústí n.L.

Teplice

Turnov

Praha

Kladno

Mladá Boleslav

Louny

Pardubice

Kolín

Brno

deposit Hamr - Stráž

POLAND

SLOVA

KIA

AUSTRIA

GERMANY

Stráž p.R.

Liberec

Regional geology and hydrogeology

• Cenomanian, Turonian a Coniac sandstone sediments – 150-400 m thick

• Block structure: Stráž and Tlustec block separated by stráž fault zone

• Tectonic structures often filled with neovolcanic veins

• Two main aquifers – upper Turonian (unconfined), lower Cenomanian

(confined) separated by aquitard

Source: Map portal ČGS, www.geology.cz

stráž faultlugikum fault

Clay limestones and

silty claystones (low turon)

Clay siltstones of the transistory

zone cenoman-turon

Bedrock

Sandy-clay conglomerat and

lake-mudde siltstones with

the ore bodies

Multi- and middlecorny sandstones –

layers of wash-out and

friable sandstones

Characteristics of the deposits

• U – Zr – P – Ti mineralization

• Uranium minerals:

Ningyoit, uraninit, hydrozirkon,

leukoxen, coffinit, brockit

• Classification according to U-bearing

minerals:

1. ningyoit-uraninit-hydrozirkon

2. ningyoit-hydrozirkon

3. hydrozirkon

4. ningyoit

Characteristics of the deposits

Brackish Cenomanian

Marine Cenomanian

Basement

simple type complex type

Uranium mineralization Freshwater Cenomanian

Complex type

• Poorly bounded ore bodies

• Freshwater, brackish and marine Cenomanian

• Ore grade ~ 0.035 wt. % U

• Strati form post-sedimentary deposit

• U – Zr – P – Ti mineralization

• Ningyoit-uraninit-hydrozirkon type

• Hydraulic conductivity ~ 0.5-20 m/d

K ~ 0.5 – 20 m/d

Simple type

• Well bounded ore bodies

• Brackish cenomanian

• Ore grade ~ 0.056 wt. % U

Schematic cross-section of the area

weak (0.5 - 20 g/l)strong (20 - 100 g/l)

contaminationturonianwater level

cenomanianpiezometric level

crystalineschists

cenomanianaquifer

low turoniansemiaquitard

turonianaquifer

Ham

r 1 m

ine

HB

Str

áž

leach

ing

field

s

Rals

ko

NESW

1959 start of exploration works in the

north-bohemian cretaceous basin

1962 1st exploration well HJ-1

1964 – 1967 finding of sites:

Hamr, Osečná, Stráž,

Křižany (Břevniště)

1971 end of exploration

Discovery of U deposit

DH I (shaft no. 1, 2, 3, 13) 1972-1993

DK I (shaft no. 4, 5) 1983-1989

DH II (shaft no. 6, 7, 9P) -

Length of shafts: 2,246 m

Length of crosscuts: 50.5 km

Length of corridors: 37 km

Lengthof chimneys: 8 km

Volume of the fill: 4,961,000 m3

Amount of extracted ore: 10,7 mil. t

Production of U: 11,740 t

History of underground mining - overview

History of DH I

1971 initiation of DH I, start of exploitation in the area

of shafts No. 1 (227.1 m) and No. 2 (237.2 m)

1971 - 1975 drilling of the shaft No. 3 (235.4 m), building

of the backfill centres

1973 – 1975 flooding of the mine after crossing of the

tectonic fault “Anežka”

1983 - 1985 drilling of the shaft No. 13 (technical shaft

with the diameter of 6.5 m, depth 256.1 m)

1985 – 1995 Hamer Lake was released into the

underground after the volcanic flue

plummeted

History of DH II

1980 - 1988 drilling of the shaft No. 6 (305.5 m) and shaft No. 7 (307.9 m)

of the new built Mine Hamr II, exploitation never started

History of DH I

Location of DH I and DH II

History of DK I

1973 - 1976 drilling of the shaft No. 4 (281.2 m) and shaft No. 5 (268.5 m) of the

new Mine Křižany I

1983 start of exploitation

History of DK I

Location of DK I

• The main mining method was „chamber and pillar“.

• In order I, II, III, IV are mined between directional contour corridors.

The width of the chambers is 5 m, the height 4-10 m and the length 80

to 120 m.

• The ore is transported by railless

transport to chimneys, then on the ground

of cross drifts by wagons. To the surface

it is transported through shaft from where

it is transported to the mill.

• Exploited chambers are backfilled.

Mining method

Four-chamber method

Mining method

Milling and Processing Facility

1973 start of building of the mill.

Parallel building of the I. stage (1978-1980) and II. stage (1988-1991) of tailings pond with the

total area of ca. 200 ha and capacity ca. 33 mil. m3.

1979 building of the main technological facilities finished, start of the delivery track operation, start

of the verification operation.

1980-1988 permanent operation of the mill, the final maximal capacity was 800,000 t of processed

ore per year.

Milling and Processing Facility

Uranium production

Underground Uranium Mining

year

tons

1971-1993

11,740 t of Uranium

Production of chemical mill

U production – chemical mill

tons

year

1979-1994

8,152 t of Uranium

Hydraulic barrier

Principle of hydraulic barrier

Leaching fields

Piezometric water level of

cenomanian aquifer

Concentrated solutions

Hyd

rau

lic

ba

rrie

r

Treatment

U separation

Stream

drainage

Min

e H

am

r I

Mine water treatment

1971 - 1987 simple deuranization method was in operation (so called spiractors)

1988 - 2001 operation of Central Decontamination Station with treatment

capacity 30 m3 mine water per minute

Technical support activities

• Transport and mechanization plant

• Plant of technical works and construction

• Technical-supply base plant incl. siding

• Social Services Plant

• Operational laboratories

Attenuation of underground mining

1987 FMPE decision to stop construction of Hamr II - Lužice Mine and liquidation of

realized investments

1990 Government resolution No. 94/1989, declaration of attenuation at the Křižany I

Mine, start of mine disposal

1993 Government resolution No. 429/1993, declaration of attenuation at the Hamr I

Mine, cessation of mining work

1995 Government resolution No. 244/1995, announcing the implementation of the

attenuation at the Hamr I Mine, start of mine disposal

Attenuation of underground mining

1988 – 2003 Disposal of the underground and shafts No. 6 and 7 of the Mine Hamr II - Lužice

1990 - 2003 Disposal of the underground and shafts No. 4 and 5 of the Mine Křižany I

1995 - 2002 Disposal of the underground and shafts No. 1, 2, 3 and 13 of the Mine Hamr I,

658,000 m3 of the mine works was backfilled in the underground of Mine Hamr I

2001 - 2003 Controlled flooding of the Hamr I mine by tailings pond water - a total of 4.7

million m3 of alkaline (pH 9 to pH 11) tailings pond water were injected into the

underground of Mine Hamr I

Disposal of surface objects

1991 – 2009 Sequential disposal of the surface objects of the Mine Hamr II - Lužice

1992 - 2012 Sequential disposal of the surface objects of the Mine Křižany I

1990 - 2013 Sequential disposal of the surface objects of the shafts No. 1, 2 and 13

of the Mine Hamr I

1990 - 2008 Sequential disposal of the backfill centres of the Mines Hamr I and Křižany I

2014 – 2015 Disposal of the surface objects of the shaft No. 3 of the Mine Hamr I ,

decommissioning of the Central Decontamination Station and Milling and

Processing Facility

Disposal of area of Mine Křižany I - numbers

48,026 t of construction debris were recycled using a shredder

5,568 t of construction debris contaminated by radionuclides were transported to the tailings pond

554 t of scrap iron were released into the environment (ecologicaly recycled)

460 t of scrap iron contaminated by radionuclides were transported to the tailings pond

3,491 tonnes of excavated soil contaminated by radionuclides were transported to the

tailings pond

Disposal of area of Mine Křižany I

Disposal of area of shaft No. 3 of Mine Hamr I -

numbers

166,026 t of material contaminated only by radionuclides were transported to the tailings pond

2,442 t of of material contaminated by radionuclides, which, moreover, contained petroleum

hydrocarbons C10 to C40 in quantities exceeding 3000 milligrams per kilogram of dry matter,

were deprived of oil pollution by biodegradation and then stored in tailings pond

108,210 t of uncontaminated materials were used for backfilling excavations

512,000,000 Kč (20,000,000 EUR) were the costs for disposal of the surface objects of the shaft

No. 3 of the Mine Hamr I (288 mil Kč were paid from EU funds)

Disposal of area of Mine Hamr I

Disposal of CDS

The mining period took 22 years and 11,740 t of U were produced.

The disposal of underground started 1988 and finished 2003. All mines had to be backfilled

and flooded.

The disposal of surface objects started 1990 and the works were finished 2015 – it wasn’t a

priority.

Paid from the state budget with a support from EU funds.

Conclusion

Thank you for your attention