Patent Application
20140078863
In some gold mining operations the miners may not know whether gold exists in the content being mined or excavated without obtaining a sample and performing an assay, such as a fire assay, on the sample, generally at an off site location. The assay process may take multiple days and may still provide fairly limited amounts of information about the materials in the ground in the remainder of the site.
Current systems and methods for surveying a gold mine can cause undue delays in the mining operations and can be inefficient because a great deal of material may be excavated and energy may be expended only to discover gold is non-existent therein.
Time, money and energy may be saved and gold mining may be substantially more efficient and accurate through the use of efficient gold assay techniques. In view of the foregoing, the present disclosure is directed to systems and methods for assaying gold with microwave radiation.
In one exemplary embodiment, a system for assaying gold in a rock formation is provided. The system includes a transmitter configured to transmit a microwave pulse into the rock formation and an acoustic sensor coupled to the rock formation. The acoustic sensor is configured to detect an acoustic wave emitted from the rock formation in response to receipt by the rock formation of the microwave pulse.
In another exemplary embodiment, as system for assaying gold in a rock formation is provided. The system includes a transmitter configured to transmit a microwave pulse into the rock formation. The system also includes a scanner coupled to the transmitter. The scanner is configured to scan the transmitted microwave pulse over an area within which the rock formation is disposed. The system includes yet further, an acoustic sensor configured to be coupled to the rock formation. The acoustic sensor is configured to detect an acoustic wave emitted from the rock formation in response to receipt by the rock formation of the microwave pulse.
Other exemplary embodiments disclosed herein provide methods for assaying gold in a rock formation. The method includes causing transmission, via a transmitter, of a microwave pulse into the rock formation and detecting, via an acoustic sensor coupled to the rock formation, acoustic waves emitted from the rock formation in response to receipt by the rock formation of the microwave pulse.
Another exemplary embodiment provides a method of assaying gold in a rock formation. The method includes extracting rock from the rock formation. The method also includes causing transmission, via a transmitter, of a microwave pulse into the extracted rock. The method includes scanning the transmitted microwave pulse over an area within which the extracted rock is disposed and detecting, via an acoustic sensor coupled to the extracted rock, acoustic waves emitted from the extracted rock in response to receipt by the extracted rock of the microwave pulse.
It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter disclosed herein.
The skilled artisan will understand that the drawings primarily are for illustrative purposes and are not intended to limit the scope of the inventive subject matter described herein.
The features and advantages of the inventive concepts disclosed herein will become more apparent from the detailed description set forth below when taken in conjunction with the drawings.
Following below are more detailed descriptions of various concepts related to, and embodiments of, inventive apparatuses, methods, and systems for assaying gold. It should be appreciated that various concepts introduced above and discussed in greater detail below may be implemented in any of numerous ways, as the disclosed concepts are not limited to any particular manner of implementation. Examples of specific implementations and applications are provided primarily for illustrative purposes.
Various exemplary embodiments are directed generally to apparatuses methods for assaying gold in a rock formation. The concepts disclosed herein may have substantial utility in the context of gold mining applications.
Once the extracted rock formation is positioned in the beampath of the microwave pulse transmitter, which position may be indicated by one or more position indicators (including, but not limited to radar, infrared, or laser sensors) or may be manually indicated by a monitoring operator, the transmitter will be actuated to transmit a microwave pulse at the rock formation as demonstrated by step 103. Immediately after the pulse is transmitted to the rock formation, a reading may be obtained from the acoustic sensor coupled to the rock in step 104. In some embodiments, the acoustic sensor may be continuously monitored before during and after the pulse is transmitted. In some embodiments, a reading may be obtained from the acoustic sensor based on the time of transmission of the microwave pulse. In some embodiments the acoustic sensor may be electronically coupled to the transmitter to facilitate knowledge of the activation of the transmitter to transmit the pulse. The sensor may also be coupled to the transmitter such that information such as duration, frequency, and separation of the microwave pulses are transmitted to the acoustic sensor or to a processor coupled to the acoustic sensor (e.g., in a feedback loop such that the pulse duration of the transmitter may be adjusted in response to an output from the acoustic sensor). The acoustic sensor may include an ultrasonic sensor.
Once the acoustic sensor has been read, the reading may be transmitted in step 105 to a processor for further analysis and characterization of the acoustic wave. The processor may be configured to control the transmitter and the acoustic sensor. The processor may further be configured to activate each of the transmitter and the acoustic sensor so that the signal is detected at the appropriate time. As depicted in step 106, the processor may characterize the acoustic wave detected (or indicate that a wave was not detected). The characterization may involve analysis of the intensity, frequency spectrum, or phase of the acoustic wave. Values of wave parameters measured at different spatial locations may be used to determine the spatial locations or distributions of gold particles within the rock formation. The timing of the acoustic wave arrival at different spatial locations, as well as relative to the microwave pulse can also be used determine the spatial locations or distributions of gold particles within the rock formation. The characterization of the pressure wave detected by the acoustic sensor may be used by the processor in step 107 to identify the presence or the absence of gold (Au) in the extracted rock formation, as well as information concerning the amount of gold and the sizes of gold particles. Upon entering the rock, the microwaves propagate through it with some scattering and refraction, but relatively little absorption. However, when microwaves reach a metallic particle, such as gold, they induce local currents, which result in resistive heating. The amount and physical extent of this heating depends on the electromagnetic penetration of the particle, which is based on the ratio of the skin depth to the particle size. Skin depth is inversely proportional to the square root of the particle's conductivity and the microwave frequency; for gold at a 10 GHz frequency, the skin depth is ˜0.8 microns. For particles smaller than the skin depth, the microwaves penetrate and heat the whole particle at a volumetric rate of ˜σE2 volume (σ being the conductivity and E the microwave electric field). But for particles larger than the skin depth, the heating is concentrated within a skin depth deep layer on the outside of the particle, with current magnitudes high enough to exclude the field from the interior of the particle. In either event, highly conductive materials such as gold particles heat more than the surrounding rock. Over sufficiently long time periods, this heat is thermally conducted into the surrounding rock, so the gold and the rock heat to essentially the same temperature despite the fact that most of the heat is initially generated within the gold particles; this type of heating generates little acoustic signature. However, if the microwaves are delivered within a short duration time pulse, the heat deposited within a gold particle is effectively trapped there until it can diffuse out into the surrounding rock. While gold has a relatively high thermal diffusivity (˜1.30 cm2/sec), rocks have a lower diffusivity (typically ˜0.01 cm2/sec), such that thermal transport is limited by the heat's ability to escape through the rock bordering the particle. The thermal diffusion time varies approximately as Δ2/D, so a one micron gold particle takes about 1 microsecond to thermally equilibrate with its surrounding rock, while 10 micron particles require 100 microseconds. For microwave pulses shorter than the particle's thermal escape time, the heat remains trapped within the particle. If the heating is high enough, the particle can melt or even vaporize; at lower values the particle remains solid, but at a significantly higher temperature than the surrounding rock. All of these responses feature thermal expansion of the gold into the surrounding rock. The timescale of the pulse determines whether this is a smooth, acoustically fairly quiet procedure, or whether the expansion is abrupt, driving a shock wave into the rock, and generating an intense acoustic wave. The relevant timescale here is the acoustic transit time across the particle, ˜Δ/c; Δ being the particle size and c the sound speed. For a one micron gold particle, this acoustic time is ˜0.3 nanoseconds, rising to 3 nanoseconds for 10 micron particles. Accordingly, microwave heating of small gold particles within rock can lead to significant thermal disequilibrium and generate strong acoustic waves. The behavior falls into 3 general regimes, depending upon the time duration of the microwave pulse. Pulses which are longer than the thermal diffusion time (˜100 microseconds for a 10 micron particle) lead to little thermal imbalance and little acoustic signature. Pulses shorter than this, but which are still longer than the acoustic transit time (˜3 nanoseconds for 10 micron particles), do lead to elevated particle temperatures, but relatively little acoustic wave generation. However, as the pulse width becomes comparable to or shorter than the transit time, the particle does expand sharply into the surrounding rock, generating strong acoustic waves. These acoustic waves can be detected by acoustic sensors outside the rock, and used to detect and characterize the gold particles contained therein.
If the processor, determines in decision step 108 that the extracted rock formation contains gold, the rock may be transferred in step 110 to an auxiliary system such as a pulverizer for further extraction of the gold from the rock formation. If the processor obtains a reading that indicates that no gold has been detected, the processor may adjust a parameter of the pulsed wave in step 109 such as the pulse width, pulse frequency, or pulse separation, and take a subsequent reading beginning at step 103 under the new parameter to account for prospective differences in gold particles in the rock formation that may have caused them not to be detected. The microwave frequency can be changed between low and high frequencies, hence changing the skin depth from high to low values, and thereby, for a given sized particle, changing the heat deposition from one dominated by volumetric to surface heating; the former generally exceeding the latter. Similarly, the microwave pulse width can be changed between low and high values, and thereby, for a given sized particle, changing from strong to weak acoustic wave generation, and also changing the frequency spectrum of the generated ultrasound from higher to lower values. Additionally, the processor may be configured to identify the location of a gold particle detected in the rock formation based on the characterization of the acoustic wave. The processor may also be configured to identify the size of a gold particle detected in the rock formation. In some embodiments, the processor may cause the extracted rock formation to be discarded in view of the negative reading.
While the processes shown in
Once the microwave pulse is transmitted, sensor 302 may be read to detect any pressure waves induced in rock formation 303 by gold particles disposed within rock formation 303. In some embodiments, the conveyor may be temporarily stalled such that rock remains in the line of sight of transmitter 303 for a plurality of readings. The plurality of readings may be automatic or may be initiated by a characterization of the reading from acoustic sensor 302 indicative of no gold within rock 303. In accordance with various embodiments, acoustic sensor 302 may include an ultrasonic detector. Once the appropriate microwave pulse transmission and acoustic detection has been completed rock 303 may continue to moved by conveyor 304 out of tank 307 and hence out of coupling fluid or gel 306. Based on the reading from sensor 302 the extracted rock formation may be separated into those with a positive gold reading and those with a negative gold reading. In accordance with some embodiments, a separate crane 309, which may be manually operated or may be autonomous, may be implemented to assist with the separation process. For example, crane 309 may remove rocks 303 with a negative reading from the system while allowing rocks 303 with a positive reading to pass through to a collection region for further processing. Alternatively, the crane could remove rocks 303 with a positive reading for further processing while allowing those with a negative reading to pass through to a collection region for discarding or returning to the mine.
While various inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.
The above-described embodiments of the invention can be implemented in any of numerous ways. For example, some embodiments may be implemented using hardware, software or a combination thereof. When any aspect of an embodiment is implemented at least in part in software, the software code can be executed on any suitable processor or collection of processors, whether provided in a single computer or distributed among multiple computers.
In this respect, various aspects of the invention may be embodied at least in part as a computer readable storage medium (or multiple computer readable storage media) (e.g., a computer memory, one or more floppy discs, compact discs, optical discs, magnetic tapes, flash memories, circuit configurations in Field Programmable Gate Arrays or other semiconductor devices, or other tangible computer storage medium or non-transitory medium) encoded with one or more programs that, when executed on one or more computers or other processors, perform methods that implement the various embodiments of the technology discussed above. The computer readable medium or media can be transportable, such that the program or programs stored thereon can be loaded onto one or more different computers or other processors to implement various aspects of the present technology as discussed above.
The terms “program” or “software” are used herein in a generic sense to refer to any type of computer code or set of computer-executable instructions that can be employed to program a computer or other processor to implement various aspects of the present technology as discussed above. Additionally, it should be appreciated that according to one aspect of this embodiment, one or more computer programs that when executed perform methods of the present technology need not reside on a single computer or processor, but may be distributed in a modular fashion amongst a number of different computers or processors to implement various aspects of the present technology.
Computer-executable instructions may be in many forms, such as program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Typically the functionality of the program modules may be combined or distributed as desired in various embodiments.
Also, the technology described herein may be embodied as a method, of which at least one example has been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.
The claims should not be read as limited to the described order or elements unless stated to that effect. It should be understood that various changes in form and detail may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims. All embodiments that come within the spirit and scope of the following claims and equivalents thereto are claimed.
