GISdevelopment.net ---> AARS ---> ACRS 1990 ---> Poster Session Q

Study on mineral exploration by infrared multi-spectral approach

Zhen Lanfen
Institute of Remote Sensing Application, CAS

Yang Bolin
Guiyang Institute of geological Chemistry, CAS

din Xuan
Gangzhou Institute of New Geological Technology, CAS

Tong Qingxi
Institute of Remote Sensing Application, CAS

Xue Yongqi
Shaghai Institute of Technical Physics, CAS


Abstract
In recent years, the fine split infrared multispectral scanning remote sensing technology has been newly developed for mineral exploration by the Chinese Academy of sciences. With the support of the Bureau of Earth Resources and Environment, the Chinese Academy of Sciences (CAS),several institutes of CAS cooperated closely, and used the fine-split spectral scanning remote sensing technology to acquire mineralizing alteration information, and directly to detect the gold resources in Xinjiang area. A great progress has been made and a breakthrough had been obtained. These units are ; the Institute of remote Sensing Application (Airborne Remote Sensing center), the Shanghai Institute of Technical Physics, the Guiyang Institute of Geological Chemistry, the Guangzhou Institute of New Geological Technology, the Annuli Institute of Optics and Fine Mehcanics, the Xinjiang Institute of Geography and so on. The Gold mineralized zone and mineralization are have been discovered in the western Zhunger area, Xinjiang, through a serial research procedure for mineral exploration; spectrum measurement and analysis, interpretation of satellite image, airborne remote sensing and image processing, geological engineering verification of image spectral anomaly and so on. It is reveled that the fine split infrared spectral remote sensing is a fast and effective new technology for mineral exploration, and has a vast application prospect.

Theoretical basis for file split infrared spectral scanning Remote Sensing technology on exploration
It was found by a large number of data at home and aboard that all kinds of rock and mineral component, especially alteration of rock type and intensity, spectral signature are different in the short wavelength infrared range of 2.00 - 2.50 mm; there are obvious spectral absorption features. These spectral features result from vibration of the chemical compounds combined with OH-

CO32-Al-OH Mg-OH Fe3+. NH4 etc inside components of the alteration mineral and rock. Due to vibration frequency, double frequency and compound frequency inside ions, a kind of rock or mineral usually has some absorption peaks in the band mentioned above. Therefore, according to the features, mentioned above, of different rocks and minerals, the correlation model between the fine-split spectral band and alteration types, alteration intensity can be established by the located wavelength position, width and depth of their absorption peaks as an indicator of quality and quantity Fig. 1 shows the relative reflectance curve of several typical rocks and minerals in the western Zhunger area, Xinjing.


Fig. 1 Reflectance curve of several major types of rock and mineral in the western Zhunger area, Xinjiang.

In order to make full use of fine-split infrared technology for remote sensing geological mineral exploration in the western Zhunger area, Xinjiang, a great quantity of field spectral measurement and analysis of surface features have been carried out for a number of existed gold mineral zone in test area, spectral absorption features of the major types of rock and mineral were obtained, and remote sensing spectral database in thematic geology was established in 1986.

Fine-Split infrared spectral scanning Remote Sensing technique
With the technique using the fine-split Multispectral scanner (FIMS) of the Chinese Academy of Sciences, and mounted on the imported modified Cessna Citation S/II aircrafts platform, aim of remote sensing mineral exploration will be achieved through collecting regional geological data, analysis and preliminary geological survey, selection of remote sensing bands for detecting target, flight implement image processing and analysis field verification of anomalous information and determination and assessments of the target area.
  1. Airborne fine split infrared multispectal scanner (FIMS) bands geological significances. The FIMS developed by the Shanghai Institute of Technical Physics is a thematic scanner with is specially aimed at geological remote sensing. The major technical parameters were given in Table 1.

    In the test stage of this study (1986-1987), the selected bands were mainly the six bands determined by GER corporation, USA in 1984. by test for two years and analysis of 810 groups of reflection characteristic spectral data, measured from 92 samples of rock and mineral in the western Zhunger area, Xinjiang, 2 bands of the FIMS were selected again. Their positions, widths and geological significance are listed in Table 2

    Table 1 Major technical parameters of the FIMS
    Item Parameters
    FOV 90°
    IFOV 6 m rad
    Scan rates scans/second 8
    Number of channels 12
    Spectral region 1.6 - 2.6mm
    Number of pixels per scan line 256
    Recorder On board CCT


    Table 2 selected spectral bands of FIMS and their geological significance
    No. Band Wavelength (central)
    (mm)    		 Band width
    (nm)    		 Geological significance
    1 1.600 100 Statistical important
    2 2.035 100 NH+ absorption
    3 2.087 100 Clay absorption
    4 2.143 100 Reflection of clay mineral
    5 2.200 100 Absorption of clay mineral
    6 2.205 50 OH, CO3- absorption (AI-OH)
    7 2.250 50 OH, CO3- absorption
    8 2.280 100 OH, CO3- reflection
    9 2.300 50 OH, CO3- absorption (Mg-OH)
    10 2.330 50 OH, CO3- CACO3, absorption
    11 2.380 100 OH, CO3- reflection
    12 2.450 100 OH, Mg - OH, Al-OH

  2. Image processing

    1. Pre processing

      Because the geometric and radiometric distortions are caused by the scanner in the course of collecting data, the must be pre-processed at first. There are mainly two correction ways: geometric and radiometric.

    2. Radio Method

      Ratio method is the simplest and the most frequently adopted for information extraction. It's one of the effective methods. Due to differences in information sources and selection of bands in different area, data processing would be quite different. Physically, the ratio image implicates the relative reflectance in image.

      As far as FIMS, 1/5 is quite sensitive for Kaolinite, ericite, montomorillonite and Quarte magnetize rock etc; 1/7 is for Chlorite alteration; 1/9 or 3/9 for Tal magnetite rock; 1/10 for Carbonatite, such as Calcite, Dolomite and Epidote etc.

    3. Principal component analysis

      On the FIMS image, the information correction between bands is very high; the spectral information difference of alteration rock is quire small as well. The principal component analysis is an effective method for extracting information of little differences and image decor relation, and is most frequently use din our work. Fig 2 shows the flight belts of FIMS image processed and analyzed by principal component analysis in the Hatu gold mineral area respectively in the green, red, blue image. They appear golden yellow color and are clearly discernible.

    4. Mineral absorption index (MAI) technique.

      The identification and extraction of information of altered rocks and minerals on the FIMS image depends on their obvious absorption feature in the spectral range of 2.0-2.5mm. Therefore, we have spread the Mai concept raised by Elvidge for TM image to the FIMS iagmery.


      Fig.2 Principal component analysis result of the fine-split infrared image by digital image processing. The existed Hatu gold mineral appears golden yellow colour in the image3, and is clearly discernible. Huoyanshan and Yibahuo appear the same colour in the image, and are the gold mineralized spot newly discovered.

      MAI represents the spectral deviation between the rocks with absorption features ad the rocks without absorption features, the physical quantity of soil statistical base-surface (non-altration background base-sruface) degree, namely, the absorption depth of the feature absorption band B opposite to its two shoulders (A and C).
      Base surface equation:

      af(A) + bf(B) + cf(C) + d = 0


      Among them, a, b, c, d are all coefficients

      Ai ci = Feature absorption spectral band value of two shoulders

      Bi = Features absorption spectral band grey degree value.

      By the mineral absorption indexes, the alteration information of Clay grouting, chloritization and carbonization in the FIMS image can be recognized and distinguished.

    5. Result verification

      We carried out the geological verification so as to analyze and examine the rock and mineral alteration corresponding with the anomalous hue in image. In the test area, we selected the two sites: Yibahuo and Hupyanshan to be verified. Huoyanshan is located about 10 kilometers south western of the test area. The stratum is volcanic sedimentary rock unit. The lihtological characters are composed of basalr and greenish-grey jaster rocks. The structure faults are very growth. The gold mine is characterized by auriferous quarts vein alteration. The small engineering and chemical analysis indicated that the highest gold tenor ins 12.71 g/T, the average is 5.93 g/T. preliminary scientific reserves is 64 kilograms. It's a small gold mineral body. Although it's a small scale, the efficiency of its method is confirmed. Verified result mentioned above shows that the anomalous hue points of FIMS image are well image are well coincident with the terrene alteration zoen and ore body oxidizing zone the hue anomaly in image corresponds with the existed mineral spots amounts to 57%. By the extension, we also found a new small gold mineral spot and a gold mineralization area (see fig. 2)

      In order to further verify and confirm, the efficiency of the FIMS technology on gold mineral exploration, we also selected the Bosuret test area, which is located in the center of Tuoli-Aibi Lake District. By means of processing and analysis of the FIMS image in this area, we found a new gold mineral area. Through the engineering geological exposure and preliminary evaluation, there are about 10 toms of prospective reserves 2 tons scientific reserves in this area. The auriferous quarts vein is of the highest tenor of 10 g/T., the average 2-3 g/T. Terrene quarts show that this is perspective gold mineral target area. The obvious benefit can be obtained by making use of this technology on the geological mineral exploration.
Conclusions
In recent years, the study expresses:
  1. The 2.0 - 2.5 mm technique is effective in the arid area with exposure of rock for extracting mineralization associated with geological mineral exploration, rock alteration information of country rock and the synthetic information of mineral deposit oxidize, thereby, goes ahead further for realizing the remote sensing geological chemical exploration and directly mineral exploration.

  2. The FIMS image processing and analysis must be combined closely with the analysis of miner genetic model. Rationing, principal component analysis and mineral absorption index methods are useful for the information extraction of gold mineral alteration.

  3. Due to study of FIMS technology, the relation between spectral and geological information spectral and image is closer. The study of transformation of the reflectance image has been ready for the future research and development of database and minerogenetic model specialist system analysis.

  4. The study of FIMS technique laid a foundation for the imaging spectrometer application. In this study, little discussion is given to the influence of terrain and vegetation to spectral information. But sometimes this influence is quite large in practice. Meanwhile, the gold miner genetic environment is rather complicated. The test is only the first step. The technique is similar to the geological physical and chemical exploration, and mainly provides a fast and effective method for geologists. The final evaluation on the gold mineral reserves remains to be studied further.
References
  1. Collins. W., et. al infrared airborne spectroradiometer survey results in Western Nevads area. Columbia University of applied Geophysics final report to NASA, contract JPL, 955832, 1981.

  2. Glad well, D.R; Lawrence, P: Dancziger, M. 1985 the application of rapid, semiquantiative clay mineral determination at the Cortez goldmine, Nevada. In cook, J. Chairperson; Morris Jones, D.R. Chair person et al; proceedings of the international symposium on remote sensing of environment; Remote Sensing for exploration geology, environ Res. Inst. Mich. ANN Arbor. MI, USA, P-403, (EL) 1985.

  3. Goetz A. f.H. et. al 1982 Mineral identification fro orbit; initial results from the shuttle multispectral infrared Radiometer Science. Vol 218, Dec. 3 1982

  4. Goetz A. F.H. et al 1983 Airborne imaging spectrometry; A means for director identification of surface materials. Proceedings of the 1983 international geosciences and remote sensing symposium 1983.