http://www.gisdevelopment.net/aars/acrs/1996/ts10/ts10005pf.htm

 

 

The Application of the TM data to the gold deposit prospecting

Liu Yingchun
Instute of gold Geology,
MMI, Langfang, 102800, hebei, China
Fax: +863162112454

Abstract
By foundation image manufacture, we can known the regional geologic background. Line, ring, belt mass, color are five aspects of remote sensing which could reflect the information of gold deposit. With computer, we can obtainit strata, acidic-intermediate-acidic rock body, alteration information related to gold deposit. TM data are mainly information source in polygenetic geoinformation processing of gold deposit. The prospecting models of different kinds of gold deposit are introduced in this paper.

China is a large of gold production which has almost all kinds of gold deposit, mainly being metamorphic hydrothermal -type gold deposit (eg. Jiaojia gold deposit, Jinchangyu gold deposit), magmatic hydrothermal -type gold deposit (eg. Gold deposits in Xiaoqingling area), porphyry-type gold deposit (eg. Tuanjianguou gold deposit), bolcanic explosion -breccia-type gold deposit (eg. Qiugou gold deposit), ductile shear zone-type gold deposit (eg. Hetai gold deposit, Paishanlou gold deposit), fine disseminated -type gold deposit (eg. Yata gold deposit, which less occur in China)

All above-mentioned gold deposit types have distinctive ore-forming models and prospecting methods, However, they are with many common characteristics. Fox example, both hydrothermal-type and shear zone-type gold deposit occur in definite fracture structure with which they have close relation; Mangmatic hydrothermal -type gold deposit and volcanism-related gold deposit mainly occur in perimeter of annular structure; Fine dissemination gold deposit occur in definite strate. All gold deposit have intense alteration, and the pyretic -phallic alternation is the common alteration mineral assemblage.

The TM data have specified indication meaning about regional geologic background, structure, litho logy, strata and alteration information in gold deposit prospecting.

1. Foundation Image Manufacture
Because the TM data are the broad sheet information about 185 x 185km, We need to make a series of computer processing so that the image maked in the ground of working area can suit the demand of gold deposit geology and prospecting. Generally speaking, following aspects of work need to do.

  1. Selecting of synthetic programme: The 7,5,1 (RGB), 7,5,4 (RGB) AND 7,4,1 (RGB) are comparatively perfect in gold deposit prospecting.
  2. Morasaic image.
  3. Image amplifition.
  4. Information enhancement.
  5. Adjusting of orientation.
  6. Image sheet standardization.

2. The Auxiliary Recongnization of Strata And Lithology with Computer

  1. Lamination analysis: The image gray shade and the spatial structure are the two main recognization characteristic of image. General image processing only use the gray shade, but the lamination analysis transform the gray shade image to lamination image, in which the lamination characteristic mainly reflect the roughness of the earth surface resulted form micro-geomorphostructure, so that is can provide the information of strata and lithology and reflect the difference of the structure tensity and material components. For example, all the various lamination index image formed by the way of gray shade paragenetic matrix in north Hebei province can obviously reflect the difference of the material components in this region.
  2. Characteristic analysis: Characteristic analysis could be to obtain the information of acidic and intermediate -acidic rock body with the following methods: a: The K-L transformation of the image data in the six bands of TM 1,2,3,4,5,6. b: The synthesization of the HIS transformation of P1,P2,P3 (RGB) image, P1,P2,P3 (RGB). C: To make the HIS transformation of P1,P2,P3 (RGB) image, and to obtain the H image by the inversion of H image. d: To get the P1,P2,P3, P image by the K-L transformation of the four I,K,S, H image. e: To make the syntyesization of P1 image that could reflect the information of the acidic and intermediate -acidic rock body.

3. Alteration Information Extraction of The TM Data
Almost all gold mineralization have alteration of pyritization, limonitization, silicification and sericitization no matter what kinds of genesis of they have. We can extract the information related to gold deposit by the test of spectrum of the altered minerals.

A. Rato analysis: The spectrum test in the Dongpin gold deposit and its peripheral region in Hebei province indicate that the main latered minerals (rocks) generally have absorption valley in TM7, potassic alteration and chloritization have the characteristic of wide and weak absorption band in TM4, and two kinds of alteration index are extracted by reflectance image:

Hydroxyl index : rOH = rTM5/rTM7; Iron - stained index : rFe = rTM3/rTM4. The comprehension of two indexs of ROH and rFe indicate the alteration information of gold mineralization in the working area.

B. Characteristic principal component analysis: In the juncture area of Hunan and Jiangxi provinces, ferriferous rocks have characteristic of strong reflection in TM5 and Tm3, and strong absorption in TM4 and TM1, weak spectrum contrast between the reflection and the absorption ranging from TM4 and TM1,

Firstly, we make the principal component transformation in one group of TM1 and 3, 4,5, and then make the qualitative analysis with the transformed PCA image as far as possible to define the spectrum information image of feeriferous rocks (F image), and the PCA of F image should be suited to the following :a. TM3 -TM1 , TM3 - TM4, and TM5 - TM4 have the opposite contribution indication ; b. There is at least one intensive load in either TM3 or TM5; Secondary, we take the TM5/7 and TM4/3 as the primative band ground to define the spectrum information image of the hydroxyl -bearing minerals; Finally, we make the synthesization of F image and H image so that it could be used to indicate the alteration information of gold mineralization.

Characteristic principal component analysis need not using the method of spectrum test but referring to a part of know gold deposits (outcrops), we have develop the work of the extraction of TM alteration information and have got better effect in some regions such as Xingjiang and Liaoning provinces.

4. The Application of GIS to the TM Data and Polygenetic Geoinformation Processing of Gold Deposit

First, the TM data and the other geoinformation should be projected to unidied coordinate system - meaning of geometric registration processing; Secondly, the registration data should give imagenization to from the synthesization image data base of the polygenetic data; Finally, by the processing of the synthesixation of polyenetic image, IHS transformation and the K - L transformation, we can analysis the internal relation of gold deposit, TM data and the other polygenetic geoinformation. For example, the complex of gold geochemical prospecting anormaly and TM data could be used to find the relation between the gold mineratlization and linear or annular structure; the complex of gold anormaly, aeromagnetic data and TM data could be find the relation of gold mineralization with aeromagetic anormally gradient belt. The K-L transformation of the multi-element geochenical prospecting anormaly could be used to find the correlation gold and the other elements, etc. the complex of spatial trendency analysis image of ore-forming favouraility and remote sensing image could be directly perceived to reflect the spatial trendency variation of gold ore-forming favourability and spatial distribution of the gold prospecting.

5. Remote Sensing Prospecting Criteria And Prospecting Model Of Gold Deposit
There are five aspects of remote sensing which could reflect the information of gold deposit.

A. Line

  1. Some deep and large faulted structures controlling the boundary of tectonic units mainly show being major mega-lineament which control the distribution of gold ore -forming belts and gold mineralization centralization belts for example, the latitudinal transcrustic fracture of north laitude of 42o in Tianshan area, and the giant Tanlou fracture in the NE trend in Hunan -Jiangxi provinces.
  2. The slightly inferior regional major fracture lineament (belt) which interest the above -mentione lineaments and the intersected geologic masses always occur with ore-forming sub-belts and ore-forming regions.
  3. The inferior lineament which occur in the superimposed belts of the above-mentioned lineament belts control the distribution of the ore fields and the ore districts.
  4. The inferior lineaments which have small scale but high concentration and have relation with the comparatively larger structure are often the favourable location of occurance of he ore deposit and ore body.

B. Ring
The thermal ring fracture of magmatic emplacement and volcanic apparatus usually have close relation with gold deposits.

  1. The magmatic hydrothermal -type and the metamorphic hydrothermal-type gold depost generally occur in the periphery range of the 2-6kmof he thermal ring structure.
  2. The gold deposit which is related with volcanism are usually occur in the margin or center of the ring fracture formed by the apparatus.

C. Belt
It mainly means the host bed which generally is the remote sensing prospecting indicator of fine disseminated gold deposit.

D. Mass
It means the compression lens and lozenge - shaped structure formed by the intersection of fracture, gold despots usually occur in the pointed end of the lens and the acuteangel area of the lozenge -shaped structure-it shows that extensional are is favorable occurrence of gold deposits.

E. Colour
It mainly mean the colour tone are of strata, lithology and alteration information which is related with gold deposit.

The prospecting models of difference kinds of gold deposit are not alike, usually as following:

A. Quartz vein -type gold deposit: Complex of annular structure + deep fracture lineament belt + acuteangel area of lozenge - shaped structure + acidic and intermediate - acidic rock body + alteration information of gold mineralization + province.

B. Volcanic + type gold deposit : The volcanic - subvolcanic rocks above the old metamorphic basement series + deep linear fault mainly in NE trend + large or small annular image assemblage and the intersecting point with linear or annular small annular image assemblage and the intersecting point with linear or annular structure + geophysical - geochemical anormaly section + tectonoclastic altered rock or interstratified fracture belt. eg. Yelintou gold deposit in Zhejiang province, Qianhe gold deposit in Henan province.

C. Tectonic altered rock -type gold deposit : The complex of old terrane in special image of dark metamorphic rocks of island arc system + deep fracture and compressisonal ahear lineament belts in NE - Nne trend + multi -colour multiperiod metamorphic - migmatized - megmatic hydorthermal annular geologic body + complex of annular structure + medium geophysical - geochemical field + hydrothernmal tectonic altered rock (belt section). Eg. Jiaojia gold depoist in Shandong province.

D. Fine disseminated - type gold deposit : Linear fracture + complex of hydrothermal annular image geologic body + intersectuing joint of structure of NS and NE of NW in trend + anomalous altered fracture belt + geochemical anomaly of low - temperature assemblage. eg. Dongbeizai gold in Sichan province.