1. IAEA TM On Origin of SUD: A global perspective
Origin of gray-green sandstone and new
exploration model for Dongsheng sandstone
uranium deposit in oil-gas and coal
productive Ordos basin, China
Dr. Ziying LI
Beijing Research Institute of Uranium Geology
2012.5.29-6.1
2007.11.1-10, Trivandrum

2. IAEA TM On Origin of SUD: A global perspective
Outline
1 Geological setting
2 Unique features of the deposit
3 Origin of grey-green sandstone
4 Metallogenic and exploration model

3. 1 Geological Setting
Location:
NE of Ordos Basin in
North China
Size: 3x105 km2
Signature:
Compound basin
since palaeozoic

4. 1 Geological Setting
 Pre-Jurassic
Basements:
Archean and
Proterozoic highly
metamorphic rocks
and migmatic
granites
 Paleozoic lightly
metamorphic rocks

5. 1 Geological Setting
 Energy
resource Basin:
Oil & Gas

6. Coal and
Coal gas
C-P Coal
(Pink)
T3 Coal
(light Yellow)
J1-J2 Coal
(Yellow)

7. 1 Geological Setting
Mesozoic covers & ore beds
Series Group/ Sym. （m） Lith. Dep.
Fm.
Quat. Q ＞41 Quaternary sands and soils
Lower Zhidan K1 1780 Red and gray sandstone and
Cretaceous Group mudstone;Alluvial, fluvial and eolian origins.
Upper Fenfanghe J3f 971 conglomerate Poorly developed, Brown-red
Jurassic Fm.
Anding J2a 300 Fine-grained red or brownish red siltstone
Fm. and mudstone
Middle Zhiluo Fm. J2z 300 Gray, greenish sandstone, siltstone and U
Jurassic mudstone
Yanan Fm. J2y 450 Arkosic sandstones, siltstone and mudstone C, U
interbeds
Lower Fuxian J1f 127 Siltstone and arkosic sandstone
Jurassic Fm.
Upper Yanchang T3y >3000 Gravel-bearing sandstone with siltstone and Oil, C
Triassic Fm. mudstone interbeds

8. 1 Geological Setting
Ore Bed: Zhiluo Formation(J2)
Ore bed

9. 1 Geological Setting
Ore hosting sedimentary formation
 Sedimentary facies: Braided stream
 Lithology: Coarse-grained arkosic sandstones
 Thickness: 20 to 40 meters
 Uranium contents: 3 to 5 ppm
 Cementation: Loosely cemented.
 Ratio of sandstone to mudstone: 2:1
 Extension: stable, connected to each other
 Reducing materials: 0.5 to 1.5%.

10. Ore sedimentation sequences and lithology
Outcrop
Borehole core
Borehole core

11. Braided stream system
Uranium in
Braided
distributary
Channels

12. 1 Geological Setting
Tectonics (J)
 The Dongsheng tectonic
slope block:
dipping southwards or
SW with 2o-5o.
 Recharge-runoff-
discharge
hydrodynamic (K)
system
Dongsheng block
provided the basic
conditions for uranium
mineralization.

13. 1 Geological Setting
 Tectonics
The Zhungeerzhao-
Wangjiata Fault:
Contributions for
mineralization:
A suitable hydrodynamic
discharge regime
Generate a reducing
environment

14. 2 Unique features of the deposit
(1) Uranium mineralization controlled by the redox
zone between grey and grey-green sandstones
Greenish Sandstone
Paleo-phreatic oxid.
Interlayer oxid.
Ore body
Gray Sandstone

15. 2 Unique features of the deposit
(2) Coffinite dominant, not pitchblende
Coffinite crystal

16. 2 Unique features of the deposit
(3) Complex ore body shapes
Shape of ore body
Cross section of ore
body shape

17. 3 Origin of grey-green sandstone
Greenish sandstone originated from oil-gas
secondary reduction processes:
Secondary reduction processes: Took place
after the formation of uranium deposit
Green or gray-green sandstones: Paleo-
oxidation zone chloritization and
epidotization.

18. 3 Origin of grey-green sandstone
Mineralogical
evidence
Oxidization residual
Limonite
Pyrite

19. 3 Origin of grey-green sandstone
Geochemistry
Fe2O3/
Elements CaO CO2 S U
FeO
Greenish S. 3.96 2.83 0.04 0.41 3.4
Grey S. 1.64 1.02 0.75 0.12 14.3

20. 3 Origin of grey-green sandstone
Geochemistry
Contents of hydrocarbon( L/kg)
No. Lithology Methane Ethane Propane
Gray-green fine-
3 445 61 19
grained sandstone
Gray fine-grained
4 255 33 14
sandstone
Green medium-fine
3 620 81 23
grained sandstone
Gray medium-fine
3 257 36 13
grained sandstone

21. 3 Origin of grey-green sandstone
Abundant oil and gas in greenish
sandstones
Oil-Gas Inclusions

22. 4 Metallogenic and exploration model
It can be concluded that the uranium
mineralization mechanism of the sandstone type
uranium deposit in the northeastern Ordos Basin
is very complicated, which underwent multiple
metallogenic processes, and superposition
metallogenic & exploration model established:
Preliminary enrichment process
Paleo-phreatic oxidation process
Paleo-interlayer oxidation process
Oil-gas secondary reforming process
Thermal modification process

23. 4 Metallogenic and exploration model
Superposition metallogenic & exploration model
(A) Preliminary enrichment stage
170Ma

24. 4 Metallogenic and exploration model
Superposition metallogenic & exploration model
(B) Paleo-phreatic oxidation stage
160~135Ma

25. 4 Metallogenic and exploration model
(1)Phreatic oxidation
process(J3)
Geochemically
Vertical Zonations:
U、V、Mo、Se、
Re

26. 4 Metallogenic and exploration model
(C) Paleo-phreatic+ Paleo-interlayer
oxidation stages 125~65Ma

27. 4 Metallogenic and exploration model
U
(2) Interlayer
oxidation
process (K1-E1)
Geochemically
Horizontal Zonations:
Mo
U、V、Mo、Re 、
S…

28. 4 Metallogenic and exploration model
(2)Interlayer S
oxidation
process
Horizontal
Zonations: Shape of
U 、 V 、 Mo 、 ore body
Re、S …

29. 4 Metallogenic and exploration model
Uranium found in the redox zone: formed
by both paleo-phreatic and interlayer
oxidation processes.
ilmenite

30. Superposition metallogenic & exploration model
(D) Oil-gas +Thermal modification stages
20~8Ma

31. 4 Metallogenic and exploration model
Hydrothermal events:
Temperatures: 70oC to 170oC, Salinity from 8%
to 20%
148℃、
8.68Wt%NaCl
170℃、
3.39Wt%NaCl

32. 4 Metallogenic and exploration model
Hydrothermal process:
Hydrothermal mineral association:
Pyrite
Limonite Galena
Sphalerite

33. 4 Metallogenic and exploration model
Superposition Metallogenic Model
Superposition of metallogenic processes
Phreatic+interlayer Oxidation Oil-gas
reworking Hydrothermal reworking
Superposition of different U sources
Ore beds Provenence area Oil &Gas
Superposition of metallogenic fluids
U-bearing Water Oil-Gas Thermal Fluid

34. 4 Metallogenic and exploration model
New exploration indication
The Dongsheng deposit has unique features and
underwent complicated metallogenic processes,
among them oil-gas reforming process played
very important roles in uranium mineralization.
So correct identification on greenish sandstones
formed under paleo-oxidization and reformed
by oil-gas secondary reduction is very important
to explore for uranium deposits, especially in
those basin producing oil-gas…

35. 谢 谢
Thank you