Transcript metals in pennsylvanian black shales from ore

METALS IN PENNSYLVANIAN BLACK SHALES
METALS IN PENNSYLVANIAN BLACK SHALES
FROM ORE FLUIDS NOT FROM SEAWATER
FROM ORE FLUIDS NOT SEA WATER
sphalerite in Stark shale, N MO
rmc
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Zinc in Pennsylvanian black shales, Kansas City
The Hushpuckney black shale,
one of several metal-rich beds
in Kansas City, contains >0.2
wt % Zn (>2000 ppm).
Coveney 1979 Economic Geology
Typical metal values for metalliferous
Pennsylvanian black shales, central USA
Zn
Mo
Ba
V
U
Mecca-type shales
Heebner-type shales
>20% Corg + <1% P2O5
<20% Corg + >1% P2O5
3350
1430
300
2850
165
3020
2260
290
3170
140
1620
80
360
790
39
1930
86
190
1050
64
from Schultz & Coveney, 1991, Chemical Geology
Metalliferous Pennsylvanian black shales
contain abundant Mo.
UMV
Salina
Basin
Forest City
Basin
Illinois
Basin
Cherokee
Basin
Mo Pb
Tri-State
Arkoma
Basin
Shale Basins and MVT Ore Districts
Forest City
Basin
Salina
Basin
Illinois
Basin
Cherokee
Basin
Mo Pb
Tri-State
Arkoma
Basin
Hydrothermal dolomite + crystalline kaolinite*
* or dickite (Schroeder & Hayes 1968; Keller 1988)
1 cm
Salina
Basin
Sphalerite in Mecca Qu. Shale equiv., central MO
Sphalerite in Pennsylvanian black shales
from Coveney 1979 Economic Geology
from Coveney 1984 C.R. IX ICC
Hushpuckney Shale Mbr,
Kansas City MO
Mecca Quarry Shale Mbr,
Parke Co. IN
Sphalerite cleat in Stark Shale
sph
sph. cleat in coal
sph
1 cm
from JC Cobb, U IL dissertation, 1981
Sphalerite in coal
MVT minerals, sphalerite and kaolinite in
Pennsylvanian limestone. Stark KS
kaolinite
sphal
Bethany Falls limestone mbr., Stark, KS
hydrothermal passageways
hydrothermal passageways
Hydrothermal venting through root casts
Bethany Falls Limestone,
North Farlinville KS
or burrows
Bethany Falls Limestone
North Farlinville KS
sph
kaolinite
back
Kaolinite in hydrothermally corroded limestone
U.S. Hwy 36 Livingston Co MO
Keller’s SEM
of sugary white kaolinite in Winterset limestone,
Kansas City MO
from W.D. Keller, 1988, Clays and Clay Minerals 36,154
Mineralized tubes with dolomite,
calcite, sphalerite and kaolinite
Mineralized tubes with hydrothermal
dolomite, calcite, sphalerite and crystalline kaolinite
Bethany Falls Limestone,
Mound City KS
ferroan
dolomite
+ tr sphal.
Dolomite veinlets
I-470 Kansas City
MVT minerals in
Pennsylvanian limestone, Kansas City MO
barite
ferroan
dolomite
wall of Central United Methodist Church
A mid-Mississippian to mid-Pennylvanian
DRM or CRM paleopole
for Stark Shale fits with syngenetic magnetism
Kawasaki et al. 2007 Geophysical Journal International
Mineralization of black shales has been attributed to sea water* but this
conclusion depends on log-log plots that minimize deviations from the
central trend.
*Brongersma-Sanders 1966 Geol. Rundschau;
Heckel 1977 AAPG Bulletin;
Holland 1979 Economic Geology
Log-Log plots Mebl sh vs. Mes.w.
from HD Holland Econ. Geol. 1979
x for molybdenum
in shales and muds
Mecca Quarry shale
Carioca Trench
Black Sea
Kau Bay, Indonesia
average black shale
average shale
1500 ppm
150
77
100
100
3
Turekian and Wedepohl, 1961; Holland 1979,
1984; Calvert 1990; Middelburg 1990;
Dean et al. 1999; Zheng et al. 2000 GCA;
Th for primary fluid inclusions in
sphalerite; calcite dates (yellow)
251 Ma
136 Ma
66 Ma
39 Ma
after Coveney, Goebel & Ragan 1987 Economic Geology
Chronology for MVT ores, petroleum migration,
regional tectonics, and black shales
Pennsylvanian
black shale
deposition
Zn & Pb
ore deposition
late calcite
deposition
251 M a
53-96 o
oil
~290-251 Ma
o
o
65-122o
18-24% NNNaCl
aCl
18-24%
aCl
137 Ma
73-84o
66 Ma
oil
73-81o
10% NaCl
53-80o
0-11%
0-11% NaCl
39 Ma
52-73o
0% NaCl
0 Ma
Alleghanian orogeny etc.
Laramide Orogeny
<52 oC
0-23% NaCl
m o d e rn
300 Ma
200
100
0 Ma
from Coveney et al 2000, Geology
Sources of metals for shales
Key Facts
• Zinc, Mo and other metals are widespread in
Pennsylvanian shales.
• MVT minerals are ubiquitous throughout the
central US craton in Paleozoic strata.
• Hydrothermal sphalerite occurs in shales,
limestones, and coals of the US craton.
• Ores formed during the late Paleozoic.
• Hydrothermal fluids traversed the region for long
periods.
Zn in shale from sea water????
• No.
• More likely the Zn for sphalerite in the shales
came from the same source as the Zn in the
MVT ores, having been transported by
regional flow of basinal brines.
Hydraulic head ca. 300-250 Ma
Ouachita Mtns
A chronology for mineralization from
basinal brines in the U.S. Midcontinent
• Early venting of hydrothermal fluids to Pennsylvanian seas and
sediments with deposition of trace MVT ore and gangue minerals
in accumulating Paleozoic sediments and rocks.
• Shales, mainly gray, sealed hydrothermal systems.
• Continued hydrothermal activity plugged minor passageways and
led to formation of major ore deposits.
• Dates on calcite gangue show that sporadic migration of basinal
brines continued for >100 million years.
• Even today basinal brines from the Rockies reach central MO.
• Hydrothermal basinal brines were the sources of metals for black
shales.
Metals in Midwestern Pennsylvanian shales did not come from sea water.
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