Note: Descriptions are shown in the official language in which they were submitted.
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IN-SITU LEACHING OF ORE DEPOSITS LOCATED IN IMPERMEABLE
UNDERGROUND FORMATIONS
FIELD OF THE INVENTION
[001] The present invention relates generally to mining ore, and more
particularly,
relating to a method of in-situ leaching of uranium deposits located in non-
porous,
impermeable underground formations.
BACKGROUND OF THE INVENTION
[002] Currently, uranium deposits are mined using open-pit mining,
underground
mining, and in-situ leaching. The present application is directed toward in-
situ
leaching. In-situ leaching (ISL), also referred to as solution mining, is well-
known, and example methods are described in U.S. Patent Nos. 3,309,140;
4,185,872; 4,239,286; and 4,285,548, the entirety of each are incorporated
herein
by reference. Generally speaking, in-situ leaching is a process where uranium
is
recovered from an underground deposit through wellbores that are drilled into
the
deposit. A leaching solution is pumped into the deposit to dissolve the
uranium
and is then pumped to the surface where the solution is processed to separate
the
uranium from the solution.
[003] In-situ leaching mining of uranium is preferred over the other mining
methods for
several reasons. These reasons include lower development and operating costs,
reduced hazard to workers, smaller work force, and less expensive remediation,
among others. Currently, in-situ leaching of uranium is performed on deposits
located in sedimentary rock formations due to the natural porosity and
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permeability of sedimentary rock. While current mining is limited to
sedimentary
rock formations, there are significant uranium deposits located in non-
sedimentary rock formations. These include deposits located in non-porous,
impermeable metamorphic and igneous rock formations.
[004] The industry has avoided these deposits because in-situ leaching
requires a
porous, permeable formation so that the leaching solution can flow through the
formation to dissolve the uranium. According, there is a need for in-situ
leaching
of uranium deposits located in underground formations of non-porous,
impermeable rock, such as, metamorphic or igneous rock formations.
SUMMARY OF THE INVENTION
[005] Embodiments of the present invention provide a method and system of in-
situ
leaching of ore deposits located in impermeable underground formations. These
underground formations include non-porous and impermeable igneous or
metamorphic rock, for example, that contain valuable ore deposits, such as
uranium that heretofore have not been recovered by in-situ leaching.
[006] In general, in one aspect, a method of in-situ recovery of uranium
disposed in an
underground formation comprising non-porous impermeable rock includes:
a) hydraulically fracturing the underground formation, thereby creating a
fractured zone along said uranium deposit;
b) introducing a flowable explosive into said fractured zone;
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c) detonating said explosive, thereby creating a permeable zone;
d) injecting a recovery solution into said permeable zone; and
e) recovering said recovery solution from said permeable zone.
[007] There has thus been outlined, rather broadly, the more important
features of the
invention in order that the detailed description thereof that follows may be
better
understood and in order that the present contribution to the art may be better
appreciated.
BRIEF DESCRIPTION OF THE DRAWINGS
[008] In the drawings:
[009] Figure I is a cross-section of an in-situ leaching mine constructed
in accordance
with an embodiment of the present invention;
[010] Figure 2 is a flow chart illustrating a method of forming a permeable
zone within
a non-permeable formation in accordance with an embodiment of the invention;
[011] Figure 3 is a cross-section of an underground formation after the
underground
formation has been hydraulically fractured in accordance with an embodiment of
the present invention; and
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[012] Figure 4 is a cross-section of an underground formation after
detonation of an
explosive within a fractured zone of the underground formation, creating a
permeable zone in the formation.
DETAILED DESCRIPTION OF THE INVENTION
[013] Embodiments of the present invention provide an in-situ leaching
mining method
for the recovery of ore deposits located within underground formations
comprising non-porous and impermeable rock, such as igneous and metamorphic
rock formations.
[014] With reference to FIG. 1, there is illustrated a cross-section of an
in-situ leaching
mine 100 operating to recover ore deposit 102, such as uranium, located within
underground formation 104 that has been constructed in accordance with an
embodiment of the present invention. Conventionally, leaching solution 106 is
injected into the underground formation 104 through injection well 108. Then
after flowing through the underground formation 104, ore rich solution 110 is
recovered at the surface from the underground formation through production
wells 112. In practice, the mine 100 may include any number of configurations
of
injection wells and production wells based upon the geologic formation
containing the ore deposit 102.
[015] Unconventionally, the underground formation 104 containing the ore
deposit 102
is a non-porous and impermeable rock formation that has been operated upon
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using the methods disclosed herein such that the ore can be recovered from the
formation utilizing conventional in-situ leaching techniques.
[016] Particularly, the methods disclosed herein create a highly porous and
permeable
zone 114 in the underground formation 104 along the ore deposit 102 such that
an
in-situ leaching mining process can be performed to extract the ore deposit
from
the formation that otherwise would not be possible. For illustrative and
discussion
purposes only, zone 114 is shown entirely disposed within the ore deposit 102.
But, in practice, one of ordinary skill would readily appreciate that zone 114
could be formed in many different configurations to achieve desired in-situ
leaching of the ore deposit. As a non-limiting example, zone 114 could be
created
so as to entirely encompass the ore deposit 102.
[017] In FIG. 2, a flow chart illustrates a method 200 according to an
embodiment of
the invention. At step 202, a borehole or multiple boreholes are drilled into
the
formation as determined based upon various factors, including geology of the
formation and ore deposit. At step 204, after the one or more boreholes are
formed, a hydraulic fracturing operation is performed on the formation
utilizing
one or more of the previously formed boreholes to fracture the formation and
create one or more fracture zones. For the purpose of herein, hydraulic
fracturing,
hydrofracking, fracking, or hydroshearing meaning forcing opening of fissures
in
the underground formation. Further, one of ordinary skill in the art will
readily
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appreciate that any number of known hydraulic fracturing methods can be used
according to the geology of the formation
[018] At step 206, after fracturing the formation, a flowable explosive is
introduced into
the fractured formation through one or more of the boreholes and is caused to
flow into the fissures of the one or more fracture zones that were formed in
the
formation during the prior fracturing operation. For the purpose of herein,
flowable explosive means any explosive material that can be pumped or
otherwise
caused to flow into the formation. As a non-limiting example, nitroglycerine,
astrolite, and nitromethane are types of flowable explosives that may be used.
Additionally, the flowable explosive could be granular or a liquid mixed with
a
granular. Finally, it is important to note that step 206 must be performed
after step
204 to form the fissures that the explosive is caused to fill.
[019] At step 208, after the flowable explosive is introduced into the one
or more
fracture zones, the explosive is detonated causing further fracturing of the
formation or otherwise rubblization of the fracture zones, thereby forming
permeable zones. For the purpose of herein, rubblization means fragmenting the
formation into a finer-grain matrix that has a high permeability than the
formation
beyond the rubblized zone. Detonating the fracture zones may cause one or more
of the boreholes formed in step 202 to collapse which may need to be
reestablish
as desired for the completion of the in-situ leaching mine. And steps 202
through
208 may be repeated as necessary to complete development of the mine.
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[020] After the forgoing method has been completed on the underground
formation, the
in-situ leaching mine can be completed according to known methods by
completing leaching solution injection wells and solution recovery wells
according the site plan as developed according the geology of the formation
and
the ore deposit. In certain instances the one or more bores formed during step
202
may be completed either as injection or recovery wells based upon the site
plan
and the geology of the formation and ore deposit.
[021] With reference to FIG. 3, there is representatively illustrated an
enlarged, cross-
section of an underground formation after the underground formation has been
hydraulically fractured, for example as in step 204 discussed above.
Particularly,
borehole 302 has been drilled into the formation 304, and as illustrated, also
into
the ore deposit 306 that is located within the formation. As further
illustrated, the
formation along ore deposit 306 includes a fracture zone, generally indicated
by
broken line 308, which includes numerous fissures 310 formed into the
formation
during the fracturing step.
[022] With reference to FIG. 4, there is representatively illustrated an
enlarged, cross-
section of an underground formation after detonation of the explosive, for
example as in step 208 discussed above. Particularly, the fracture zone, such
as
fracture zone 308 of FIG. 3, has been rubbilized by detonation of the
explosive,
thereby creating a permeable zone 402 in the underground formation 404 along
the ore deposit 406. In the permeable zone 402, the formation has been
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fragmented into a finer-grain matrix of rubble 408 that allows in-situ
leaching of
the ore located in the permeable zone. As further illustrated, borehole 410
has
been reestablished and may be further completed as either a leaching solution
injection well or a leaching solution recovery well.
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