A BIM BOP, BAM:{ Still waiting for GAAH BOOM! }( Say...Salt / Sulfate ENCAPSULATION and see this REDOX mention below-{{..Where fractures or faults permit vertical fluid migration, fluids and rocks
of contrasting redox potentials co-mingle and conditions for the deposition
of magnetic minerals may exist. Precipitation of magnetic minerals by redox
reactions is enhanced by the presence of sulfur and hydrocarbons in the
rock-fluid system...}}..and think of Bob Barefoot of DCRS! THE Great Basin Gold Discovery Theses 1994)
I search the WWW for two TERMs in the Recent 7 pages of Text Data in the BMD NR on 7-16-1999 and the first set came up empty, MOBERLY MEMBER( Anyone ? Help more later on that - proberly in my Geo Textbooks) and then, WATERWAYS FORMATIONS so, VOILA Dr Huge Amercrombie's ThesEs as a Report on Waterways Formation :
ucalgary.ca
University of Calgary
Department of Geology and Geophysics
Theses
THESES unless otherwised noted are located in GEO-THESES and are available for a 1WEEK loan period.
Abercrombie, Hugh J., Water-rock interaction during diagenesis and thermal recovery, Cold Lake, Alberta. Ph.D. 1988.
(Canadian theses number: ISBN 0315502843) QE431.6 .W38 A23 1988
another hit:
civil.ualberta.ca
1983 Heald, B.D. A Geotechnical Investigation of the Devonian Waterways Formation at the Sandalta Lease
(Supervisor: Dr. D.M. Cruden)
Now Mid Devonian which is THE MISSISSIPPIAM AGE:
gedco.com
Figure 1. (top) Authigenic pyrrhotite seen in polished thin section in sample
taken from 75 m depth, drill hole ATH 94-01, Lac Minerals. The image
length is 4 mm. Pyrrhotite locally makes up 1-5% of the calcareous shales
of the Waterways Formation (Mid. - Upper Devonian) in NE Alberta. The
presence of authigenic pyrrhotite is interpreted to indicate highly reducing
conditions associated with bacterial sulfate reduction (BSR) in upflow
zones.
Figure 2. (bottom) Native sulfur crystals line a vertical fracture in
bituminous laminites of the Methy (Winnipegosis) Formation, NE Alberta
(sample from 291.8 m depth, drill hole ATH 94-03, Lac Minerals). Native
sulfur records fracture controlled inflow of saline brines and reduction of
sulfate.
Chucka - nice pictures, also- NE Alberta
P.S.-The BEST: Dr Huge Abercrombie ( they Misspelt it below )
From his E Mail Bisness Card that he sent me last month, it is now revised correct, I had asked him about Mississippian and this may help explain as per his response:( no specific BM questions- just geology in general, so OK here I think)
Dr A said:
MVT/Dolomite ..."Later, higher temperature dolomitization often results in destruction of depositional textures and formation of coarsely crystalline, white dolomite (sparry dolomite) associated with MVT deposits. Just my thoughts..."
I Asked-Huge, MVT..>>
gedco.com
INTRA-SEDIMENTARY MAGNETIZATION OF THE HINES
CREEK FAULT (N. ALBERTA) BY VERTICAL FLUID FLOW
AND EXOTIC GEOCHEMISTRY
John W. Peirce*1, Hugh J. Abercrombi2, Glen R. DePaoli2, Serguei A.
Goussev1 and Robert A. Charters1,
Geophysical Exploration & Development Corporation (GEDCO);1
Birch Mountain Resources Ltd., 2 Consultant
Published in slightly different form in The Leading Edge, January,
1998, pp. 89-92.
SUMMARY
A seismic line crossing the Hines Creek Fault with magnetic depth solutions
plotted in time as an overlay shows a remarkable correspondence between
the position of intra-sedimentary magnetic depth solutions and the position
of the seismically imaged fault trace. This one-to-one correlation clearly
demonstrates that the region immediately around the fault plane is
magnetized.
We propose a model involving vertical flow of fluids along fractures and
faults to explain the observed magnetization along fault planes detected by
High Resolution AeroMagnetic (HRAM) surveys. This model involves the
transport of iron in oxidized waters flowing along vertical fractures near
basement and the precipitation of exotic iron-bearing minerals during ascent
of the water as it undergoes redox reactions within the fracture system.
INTRODUCTIONS AND HYPOTHESIS
New HRAM surveys have been or are being flown during 1994-1997 over
the majority of the Western Canada S edimentary Basin south of 610 and
Canadian portions of the Williston Basin. This case history covers a portion
of the Peace River Arch (Twp 78-87, Rge 1-3 W6) and demonstrates one
approach to interpreting these new data.
Since the mid 1980's evidence has been accumulating that
intra-sedimentary fault planes are sometimes magnetized sufficiently to
detect from airborne surveys (e.g., Jain, 1986), but unarguable evidence
has been very sparse in the literature. Our recent work (e.g., Ebner et al.,
1995; Peirce et al., in press) has convinced us that fluid flow along fractures
and fault planes is the underlying cause of such magnetization.
OBSERVATIONS
1. Regional hydrodynamic studies of the Alberta Basin show that there is
widespread potential for vertical migration of fluids (Rakhit et al., 1996).
For the most part, however, this is unrealized because of the presence of
laterally extensive low vertical permeability strata such as shales and
evaporites.
2. Fractures and faults provide one of the few mechanisms to move fluids
across regional scale, laterally continuous barriers to vertical migration.
3. Where fractures or faults permit vertical fluid migration, fluids and rocks
of contrasting redox potentials co-mingle and conditions for the deposition
of magnetic minerals may exist. Precipitation of magnetic minerals by redox
reactions is enhanced by the presence of sulfur and hydrocarbons in the
rock-fluid system.
4. Studies of Paleozoic cores in NE Alberta have shown that there has
been vertical migration of sulfate rich waters in the presence of
hydrocarbons from the oxidizing environment of the Devonian Elk Point
Group into overlying reduced calcareous shales of the Devonian Beaverhill
Lake Group. This fluid migration has caused the low temperature formation
of exotic mineral species such as pyrrhotite and pentlandite in the Beaverhill
Lake Group Figure 1 and native sulfur in bituminous laminites of the Methy
Formation Figure 2 in NE Alberta.
5. Detailed magnetic depth analyses done on a profile by profile basis
detect vertically oriented patterns of depth solutions which can be
correlated over several flight lines for distances of kilometers (Jain, 1986;
Peirce et al., in press). In some cases these vertical alignments of depth
solutions have been correlated to seismically defined faults.
APPROACH
Our approach is to interpret every profile from HRAM surveys using
detailed Werner and 2D Euler depth analysis using MagprobeTM software
in batch mode. Vertical alignments of depth solutions are common within
both the sedimentary section and within the basement when the parameters
are set appropriately. We interpret these vertical alignments of depth
solutions as faults or fractures. The same analyses also provide estimates to
the top of magnetic basement. We use filtered versions of the gridded
magnetic data to help us correlate faults between flight lines, and the
resulting product is a structural grain map. We usually produce one
intra-sedimentary structural grain map and one basement structural grain
map. On the basement map we also combine the available deep well
control with magnetic depth estimates to produce contours of the depth to
crystalline (magnetic) basement, which is usually (but not always) the same
as the Precambrian surface. The final basement map has more detail than
can be made from the well control alone, and the contouring reflects the
structural grain derived from the faults seen on the depth profiles. This
approach has proved effective at finding basement-related structural leads
which have later been confirmed by seismic methods.
EXAMPLE
In the Hines Creek case history at least five areas of structural closure are
highlighted in a 33 Twp area. The shapes and sizes of these closures are
quite different from those based on well control alone, and they can be
related to the regional structural grain of faults and fractures.
A seismic line crossing the Hines Creek Fault provided a clear example of a
large basement offset with an overlying intra-sedimentary fault extending up
into the Cretaceous section. Magnetically, this portion of the Hines Creek
Fault system is very clearly seen on high frequency filtered versions of the
magnetic data. On a profile basis there is no clear separation between the
anomaly caused by the basement offset and anomalous effects caused by
intra-sedimentary magnetization. However, on the MagprobeTM section
there is a intra-basement set of depth solutions and a distinctly separate set
of depth solutions (with vertical dips) related to the fault at depths 400 m
above basement. When the depth solutions are plotted in seismic travel time
as an overlay on the seismic section Figure 3 there is a very close
correspondence (+/- 150 m) between the position of the depth solutions
and the seismic image of the fault offset.
This remarkable correspondence between the seismic and magnetic images
of the fault is, in our opinion, the "smoking gun" piece of evidence that
demonstrates inarguably that some fault planes are magnetized. Our
experience to date suggests that perhaps only 25% of the seismically visible
faults can be detected magnetically using this approach. However, we also
see numerous fractures magnetically which are not detected seismically,
presumably because there is no significant offset on the fracture. More
direct comparisons between seismic and magnetics are needed to refine this
initial estimate.
GEOCHEMICAL MODEL
Rocks of the Alberta Basin are representative of deposition under a variety
of redox conditions. These range from the highly oxidizing conditions
prevailing during deposition of evaporites to the highly reducing conditions
during deposition of anoxic marine shales. Burial and generation of
hydrocarbons introduces another reduced component into the basin. Sulfur
is a convenient indicator of redox conditions because of its multiple valence
states (-2 to +6) and its participation in redox reactions at virtually all
temperatures.
This geochemical model below is based on evidence from NE Alberta,
about 400 km east of the Hines Creek Fault. We believe that the processes
described in the geochemical model are general and are applicable in any
hydrocarbon-rich basin.
A simplified geochemical model for redox relations amongst iron and sulfur
aqueous and mineral species has been calculated. The variable "logf(O2)" is
the logarithm of oxygen fugacity (similar to partial pressure, but corrected
for non-ideal behavior of O2 gas) and is a geochemical representation of
the redox state of the system under consideration. Thus, greater (less
negative) values of logf(O2) indicate more oxidized conditions. For
example, surface water in equilibrium with atmospheric oxygen has a
logf(O2) value =~ -3.6. By comparison, pyrrhotite forms only at oxygen
fugacities below -60.
The phase diagram shows that the redox state of a rock can be estimated
by its mineralogy. For example, a red bed-evaporite system with abundant
hematite and anhydrite represents a more oxidized environment than a
marine evaporite containing pyrite and anhydrite. Pyrrhotite is the most
reduced iron bearing mineral in this system. Its occurrence within the
calcareous shales of the Waterways Formation is unusual and is explained
by bacterial sulfate reduction (BSR) in the presence of hydrocarbons.
Because the stability field for pyrrhotite lies below the lower limit of calcite
stability we know that this example of pyrrhotite formation is not a bulk
rock process. Similarly, the presence of native sulfur in fractures within the
Methy and Waterways Formations indicates that fractures are the preferred
site for deposition of exotic minerals by redox processes induced by
vertical flow of waters of contrasting redox state. Stratigraphic and redox
relations in NE Alberta are schematically illustrated in Figure 4.
At temperatures greater than approximately 1200C BSR is no longer
important and the sulfate reduction reaction proceeds spontaneously
through thermochemical sulfate reduction (TSR) (Goldhaber and Orr,
1995). This process is responsible for the generation of large volumes of
H2S in deep reservoirs. We suggest that TSR is likely to occur in deeper
fractures if sulfate and hydrocarbons come in contact through vertical
movement of fluids. For reasons similar to those outlined for NE Alberta,
we hypothesize that deeper seated redox reactions are likely to occur in
fractures and result in deposition of iron-bearing minerals with a wide range
of susceptibilities. Thus redox-controlled fracture mineralization of
iron-bearing species may be an explanation for intra-sedimentary
magnetization associated with regions of reactivated basement faulting.
CONCLUSIONS
The seismic and magnetic evidence demonstrate that part of one fault in the
Hines Creek Fault system is magnetized within the sedimentary section and
the basement over a lateral distance of 12 km. We believe that the
sedimentary magnetization is caused by exotic geochemical reactions
involving iron, sulfur compounds and hydrocarbons. These reactions can
precipitate magnetic minerals under favorable redox conditions. Bacterial
catalysis may enhance the formation of unexpected mineralogy such as
authigenic pyrrhotite at shallow depths.
ACKNOWLEDGEMENTS
We would like to acknowledge John Gorveatt of Varidata Surveys Ltd. for
helping in locating the example seismic line, Zig Doborzinski of Imperial Oil
Resources Ltd. for providing the seismic line, and Joan Likuski of Seiscraft
Processing Inc. for reprocessing the seismic line.
1 GEDCO, Suite 1200, 815-8th Avenue SW, Calgary, Alberta T2P
3P2,Canada
2 Birch Mountain Resources Ltd., Suite 3100, 205-5th Avenue SW,
Calgary, Alberta T2P 3P2, Canada
See REFERENCES
Contact John Peirce at GEDCO with any comments you may have
.
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