Norsk versjon
THE ORE DATABASE
Deposit Area 1742 - 003
(Last updated 15.mai.2006)

Name of Deposit Area : Broka
(Object Id : 1742,003,00,00)
Location
County : Nord-Trøndelag (17) Municipality : Grong (1742)
Map 1:50000: Grong (1823-4) Map 1:250000: Grong
Marking point: Longitude: 12.6085340 Latitude: 64.4614200
EU89-UTM Zone 33 (Coordinates IS confirmed)
X-coord: 384981 m. Y-coord: 7150599 m.
Commodity
Main Type: Base metals (Cu,Zn,Pb,Fe sulphides, As,Sb,Bi,Sn) Sub Type: Sulphides
Element(s): Kis
Production
Activity: Pitting Reserves:
Prod. method: Production:
Prod. status: Volume of dump: 0 m3

Importance
Public: Little Importance (reg. 18.02.2015)
Economical: Minor interest

Operations
From - To Activity Comments
1980 - 1980 Geology Company/Institution :Grong Gruber A/S
1980 - 1980 Geochemistry Company/Institution :Grong Gruber A/S
1991 - 1991 Sampling Company/Institution :NGU
1996 - 1996 Inspection Company/Institution :NGU

Mineralization
Era: Paleozoic Period: Ordovician
Dating: Method:
Genesis: Volcex Form: Layer
Main texture: Structureless Min. distribution: Massive (>50 % ore minerals)
Main grain size: Fine grained (< 1 mm) Main alteration: No country rock alteration
Strike/Dip: 260 / 80 Direction:
Plunge:
Stratigraphic classification of host rock
Era: Paleozoic Period: Ordovician
Province: Caledonides
Geotec.unit: Køli Nappe Complex
Tectonic complex: Gjersvik Nappe
Igneous complex:
Group: Gjersvik Formation:

Mineralogy
Relationship Mineral Amount
Gangue mineral Quartz Major mineral (>10%)
Gangue mineral Chlorite Subordinate mineral (1-10%)
Ore mineral Pyrite Major mineral (>10%)

Lithology:
Relationship Rock Origin
Wall rock Greenschist Sedimentary
Original rock :Tuffite
Metamorphic facies :Greenschist
Wall rock Quartz-amphibole gneiss Sedimentary
Original rock :Tuffite
Metamorphic facies :Greenschist

Structures
Location: Type: Orientation(360 gr.): Relation to min.:
Wall rock Foliation Strike/Dip :252 / 65 Post-mineralisation ;...Effect :Modifies
Wall rock Schistosity Strike/Dip :255 / 80 Post-mineralisation ;...Effect :None

Information(s) in free text format
Free text
Forekomsten ligger i bekken 100 m nedenfor utløpet fra Broka, og kan nåes fra skogsbilvei fra Stortjønna i sør. En ca. 20 cm mektig massiv svovelkissone med kvartsførende matriks er blottet langs bekken. Basemetallinnholdet er lavt. Kvartsrik gneis med amfibolbånd finnes i tektonostratigrafisk ligg, mens grønnskifer opptrer i heng. Geofysiske målinger viser at den elektrisk ledende sonen fortsetter 2 km langs strøket både mot øst og vest. Mineraliseringen opptrer trolig innenfor samme stratigrafiske enhet som forekomstene Godejord og Finnbu.

Bibliography:
From NGU's Reference Archive:
Oftedahl, Christoffer , 1958
Oversikt over Grongfeltets skjerp og malmforekomster.
;Norges geologiske undersøkelse;TIDSSKRIFTARTIKKEL;NGU; No.202;1-75 + fo pages
Abstract:
Ore occurences of the Grong area: In the period 1910-1918 a great number of ore occurences were discovered in the Grong area. The late state geologist Steinar Foslie mapped the area in the years 1922-1931. Foslie also mapped all claims and occurences and made special field investigations in a few cases. This book presents a survey of all occurences chiefly based on the field observations of Foslie. In addition the present author has done some field work in connection with the three large deposits, Joma, Skorovass, and Gjersvik. The map, Plate 1, shows the areal geology and the location of the occurrences, numbered from 1 to 131. the ore of the occurrences is chiefly pyrite. The larger occurrences also contain some chalcopyrite and sphalerite etc. and the smaller occurrences contain ither pure pyrite with some magnetite. The Joma deposit (No. 1), contains about 15.5 mill. tons of ore. The ore zone forms an arc and is situated within a thick series of greenstones (Fig. 1). The Skorovass mine (No. 2), contains about 7,5 mill. tons of ore. The deposit is situated in a greenstone complex (Fig. 7), and is immediately surrounded by asid tuffs of quartz keratophyric composition (Table 1).

Olesen, Odleiv , 1980
Oppfølging av områder med malmpotensial i Grongfeltet.
;NTH Bergavd.;AVHANDLING

Fieldsamples
Sample No. Sample type Miscellanrous
gr0307 Bedrock
Sampler :Sandstad, J.S.
Comment :Pyrrhotite-pyrite, massive ore, fine grained, quartz rich fragments, few quartz veinlets.
No. of registrated element analyses = 1
1140 Bedrock
No. of registrated element analyses = 1
1141 Bedrock
No. of registrated element analyses = 1
1142 Bedrock
No. of registrated element analyses = 1
1143 Bedrock
No. of registrated element analyses = 1
1144 Bedrock
No. of registrated element analyses = 1
NB! All analyse values are shown at the end of the printout.:

Analyse Results
from
Deposit Area 1742 - 003 Broka

Element analyses
( *=parts pr. million, #=parts pr.billion, Negative values means below detection limit value.)
Sample No. Sample Type Cu* Zn* Pb* Co* Ni* Ag* Au#
gr0307 Bedrock 232 399 14 18 48 .3 17.0
1140 Bedrock 77 528 8 15 27 .1 21.0
1141 Bedrock 257 1013 2 15 58 .4 12.0
1142 Bedrock 237 373 2 14 67 .3 18.0
1143 Bedrock 243 722 4 16 59 .4 15.0
1144 Bedrock 262 926 8 14 51 .2 11.0
------------------
Sample No. Pt# Pd# As* Cd* Ba* Mo* Sb* Bi* S%
gr0307 2.0 3.0 163 3.2 11 1.00 2 2 28.20
1140 3.0 5.0 184 3.3 8 2.00 2 5 31.43
1141 2.0 2.0 225 4.6 12 1.00 2 2 30.81
1142 4.0 6.0 173 .6 14 1.00 2 2 34.52
1143 4.0 8.0 170 3.2 10 1.00 2 2 36.18
1144 5.0 5.0 204 3.7 12 1.00 2 5 32.47
------------------
Sample No. V* Cr* Mn* Fe% Th* U* W* Sr* La*
gr0307 51 30 465 22.07 2.00 8.00 1 6.0 4.00
1140 43 6 96 21.48 1.00 5.00 1 1.0 3.00
1141 22 2 253 32.26 3.00 5.00 1 5.0 3.00
1142 12 1 100 34.37 2.00 5.00 1 2.0 2.00
1143 28 3 120 30.95 3.00 5.00 1 3.0 3.00
1144 22 1 293 28.90 2.00 9.00 1 5.0 3.00
------------------
Sample No. B*
gr0307 19
1140 2
1141 2
1142 2
1143 2
1144 2

The fact sheet was created on 16.01.2025
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