Evaluation of Landsat multispectral scanner images for mapping altered rocks in the East Tintic Mountains, Utah
<p>The East Tintic Mountains, Utah consist of folded and faulted Paleozoic sedimentary rocks, which are partly covered by Tertiary volcanic rocks. Clastic…
Public-domain full text preserved in the Mountain Man Mining Library. Original source: pubs.usgs.gov.
s[J-7/ LA
EVALUATION OF LANDSAT MULTISPECTRAL SCANNER IMAGES FOR MAPPING ALTERED ROCKS IN THE EAST TINTIC MOUNTAINS, UTAH by Lawrence C. Rowan, U. S. Geological Survey, Reston, Vir coLOGICAL S. co.sT ON, 41,44fr, and FEB 1 6 1979 ,k & R Michael J.°Abrams Jet Propulsion Laboratory, Pasadena, California f/ U. S. Geological Survey, Open File Report 78-735
Table of Contents Page Abstract Introduction Acknowledgements Lithology Sedimentary rocks Igneous rocks Hydrothermally altered rocks Vegetation Spectral reflectance Image analysis Color photographs MSS images Individual MSS band images Color-ratio composite images Evaluation of limonitic bedrock map East Tintic mining district Conclusions References cited
List of Figures Page Figure 1 - Index map of the Great. Basin lA Figure 2 - Index map of the central part of the East Tintic Mountains 1B Figure 3 - Generalized geologic map 2A Figure 4 - Map of silicified rocks, veins and dikes 18A Figure 5 - Alteration map of the East Tintic Mining District 20A Figure 6 - Representative in situ reflectance spectra for unaltered and weathered quartz latite 31A Figure 7 - Representative in situ reflectance spectra for quartz latite subjected to accelerated weathering . 32A Figure 8 - Representative in situ reflectance spectra for calcitic quartz latite 33A Figure 9 - Representative in situ reflectance spectra for argillized latitic tuff 33B Figure 10 - Representative in situ reflectance spectra for argillized latitic tuff 34A Figure 11 - Representative in situ reflectance spectra for argillized quartz latitic tuff 34B Figure 12 - Representative in situ reflectance spectra for intensely argillized quartz latite tuffs and flows . 35A
Page Figure 13 - Representative in situ reflectance spectra for silicified rocks 35B Figure 14 - Representative in situ reflectance spectra for limestones 36A Figure 15 - Representative in situ reflectance spectra for dolomites 37A Figure 16 - Representative in situ reflectance spectra for sage and juniper 38A Figure 17 - Skylab S190-B color photograph 41A Figure 18 - High-altitude color photograph 42A Figure 19 - Linearly stretched MSS band 5 image 46A Figure 20 - Density sliced MSS band 5 image 47A Figure 21 - Color-infrared composite image 49A Figure 22 - Schematic fraquency distributions for MSS ratios 4/5, 5/6, 6/7, and 4/6 52A Figure 23 - Color-ratio composite image SSA Figure 24 - Map showing the distribution of green pixels. 55B Figure 25 - Map showing distribution of green pixels representing limonitic bedrock SSC Figure 26 - Map comparing altered rocks mapped in the field with pixels representing limonitic bedrock 56A Figure 27 - Limonitic bedrock map of the East Tintic mining district 66A Figure 28 - Low-altitude color photograph of the East Tintic mining district 67A
List of Tables Page Table 1 - Brief descriptions of geologic units . . . SA Table 2 - Paragenesis of alteration and ore minerals 21A Table 3 - Parameters for linear stretches used for black-andwhite MSS images of the study area 54A
Evaluation of Landsat Multispectral Scanner Images For Mapping Altered Rocks in the East Tintic Mountains, Utah by Lawrence C. Rowan, U.S. Geological. Survey, Reston, VA Michael J. Abrams, Jet Propulsion Laboratory, Pasadena, CA ABSTRACT The East Tintic Mountains, Utah consist of folded and faulted Paleozoic sedimentary rocks, which are partly covered by Tertiary volcanic rocks. Clastic rocks dominate the lower one-third of the Paleozoic section, whereas carbonate rocks with subordinate amounts of shale and elastic rocks predominate in the remainder. Some of the rocks, especially the Tintic Quartzite and some shales, are commonly limonitic, an important factor in analysis of Landsat MSS images. The volcanic rocks, mainly tuffs, flows, and agglomerates of quartz latitic and latitic composition, are limonitic in a few places where hematite is present in the groundmass. Emplacement of monzonite and biotite monzonite porphyry bodies resulted in several types of altered rocks. Most widespread are argillized and silicified rocks, which are commonly bleached and limonitic. Locally, the intrusive rocks arc also altered. Hydrothermal dolomite is common in the northern part of the area, and in the East Tintic mining district, calcitic, chloritic, and weakly argillized volcanic rocks and pebble dikes are widespread. Volcanic rocks subjected to an
early phase of "intravolcanic weathering" in this district are weakly altered but commonly limonitic. Barren as well as mineralized veins are present throughout the study area. In situ spectral reflectance curves representing the most abundant altered and unaltered rocks show that the argillized and silicified rocks generally have intense ferric-iron and hydroxyl absorption bands owing to the presence of iron-oxide and hydroxyl-bearing phases, respec tively. These features are generally absent in the unaltered rocks, except the limonitic rocks, which have prominent iron absorption hands. Both spectral features are weakly expressed in the volcanic rocks subjected to accelerated weathering, On the other hand, hydrothermal dolomite and calcitic volcanic rocks generally lack both features, and thus are spectrally similar to the unaltered rocks. Chloritic rocks are of limited distribution and have not been measured spectrally. Most of the silicified and argillized areas are apparent in Skylab S190B, high altitude-, and low altitude color aerial photographs because of the high albedo of these rocks. However, many unaltered rocks have similar albedos and therefore are not distinguishable from the altered rocks. Moreover, very little color information is available in these photographs. These problems are further complicated by brightness variations related to topographic slope. MSS ratio images were generated to subdue the effects of topographic slope and albedo, and combined into several color composite images for displaying the spectral reflectance differences between the most wide spread altered and unaltered rocks. The most effective combination
proved to be MSS 4/5, MSS 4/6, and MSS 6/7 using blue, yellow and magenta diazo films, respectively, rather than the MSS 4/5, MSS 5/6, and MSS 6/7 combination used so successfully in south-central Nevada. Consideration of schematic frequency distributions of ratio values for these two areas suggests that the lack of enhancement of limonitic rocks in MSS 5/6 images of the present study area is due to the higher frequency of low ratios representing vegetation. Comparison of a limonitic bedrock map produced by scanning the optimum color-ratio composite image with a map of the silicified rocks shows good agreement, except where they are obscured by vegetation. Measurements of vegetation density indicate that shrub cover and. juniper, pinyon, and sage cover greater than 40-50 and 33-43 percent, respectively, obscure limonitic rocks in these images. Argillized rocks, the most widely distributed altered rock type, were consistently detected in exposed areas. On the other hand, hydrothermal dolomite and calcitic and chloritic volcanic rocks are not portrayed in the limonitic bedrock map because of their general lack of limonite. Some altered rocks, especially veins and pebble dikes, are too small to be detected by the MSS except where they are closely spaced and well exposed. Another important limitation is that exposures of unaltered limonitic sedimentary and volcanic rocks are included in the limonitic bedrock map. Analysis of in situ spectral reflectance measurements indicates that this limitation can be largely overcome by obtaining radiance information in the 2.2 and 1.6 pm regions.
Introduction The East Tintic Mountains are a generally north-trending block faulted range in central Utah near the eastern margin of the Great Basin (fig. 1). Approximately 30,000 feet of marine sediments of late Precambrian to Permian age are asymmetrically folded and transacted by several different types of faults. These rocks, mainly carbonate, are partly overlain by Oligocene and Miocene volcanic rocks, including tuffs, agglomerates, and extensive latitic, quartz latitic, and trachy andesitic flows. Dikes, sills, and small stocks of monzonite, quartz monzonite, and latite porphyry intrude all of the volcanic series. Hydrothermal alteration associated chiefly with the Oligocene volcanic activity has affected many of these rocks. Most of the ores of the three main mining districts, the Tintic, East. Tintic, and North Tintic, occur as lead-zinc-silver replacement bodies in calcareous rocks and pyritic-copper-gold vein deposits in quartzite and the monzonite porphyry. The central part of the East Tintic Mountains (fig. 2) was selected as one of three areas for further evaluation of the colorratio composite (CRC) technique developed by Rowan and others (1974) for mapping limonitic hydrothermally altered rocks in the Goldfield region in south-central Nevada. The other areas studied during this Landsat follow-on experiment (ID No. 23890) are the Virginia Range southeast of Reno, Nevada, and the northwestern part of the Battle Mountain-Eureka mineral belt.
Figure 1 - Index map of the Great Basin showing locations of study areas: 1, East Tintic Mountains, Utah; 2, Virginia Range, Nevada; 3, Battle Mountain-Eureka mineral belt; 4, south-central Nevada.
go-V/I /1/ 200 Km
Figure 2 Index map of the central part of the East Tintic Mountains study area showing locations of cultural and topographic features, mines and prospects, and the East Tintic mining district (dashed line). 1B
SPILL 3r,uloa s , I.) 1..i 9!. - Jr* t!.
4.11.,1 R g 1J.p..bs) .01.1 'AI V;11, I IL Cut-IS (sur..) nL pins 6, l'":a f.P .u..a 4! 1113.(1 "41,.'N
P I .y191/ 1`) I w. 1 ...41":11 6'; . 11 J1,11 .bui is 1/11‘ 49'I41 14.11/19 ri
ir 111( . 9' r.; ita .19 .14.) 4.1 ..1 111)111."J Vi It' 4. 1.)('I"'.) nt ay.*, o 111,41 A it 11, Pl".".. I IP 4111W 1,1'04 ..) /AP .11/1,11 y 1104d g 111,4y I ')Ni sumu 491.1 piir 1,0011“ -.If a”: 9jui1N .111114,1/1111 Hpino ONOrr iIi it I/ SZ opryis 411.0 eiff,J pi: puow3.() Antis !I "I '".11
Amu I0,1'1 11'1 V.) lc or 1,11) .11/Iw p..1 orpos st,., u...110)1 1111.1119 97. "U' J.114.) AU11.1 1{141.1111( in/ IT. .14.119'1 R.sini XX orj„ Ja:vvS. 110104 0,0 .141.11 .1,14 11.111 I.Ir lY MIRO L ./N).1.11,1/ p11111.11,1S a %Iv. az 4titus 1,1,m4 61 map. z us) 14 311.11 tit
too, ,is ill .414.. s Lt
JNlnu p,.1 .19'19'1 ti 41741111...01 VI 11113 load .„ oisan ) s N jdois ;War:um() .01 pY11 1'Y. load suds' sts0,1 41011.0.4.0)4 ij X i°;`;-;-.7:7'41 owillo) 111
which includes Battle Mountain and the Shoshone Ranges in north-central Nevada (fig. 1). In addition, detailed studies have continued in the part of south-central Nevada previously evaluated by Rowan and others (1977). The overall objective of this Landsat Follow-on experiment was to determine the effects of several geologic and environmental factors on the ability to discriminate hydrothermally altered rocks in Landsat Mss images. The most important factors are the mineral content and spectral reflectance of the altered rocks and host rocks, type, areal density and spectral reflectance of vegetation, size of altered areas, and topographic configuration. The East Tintic Mountains provide an opportunity to examine a host rock assemblage that is substantially different from the dominantly volcanic rocks of south-central Nevada and the Virginia Range, and the siliceous, commonly ferruginous sedimentary rocks of the Battle Mountain and Shoshone Ranges. In addition, the alteration products in the East Tintic Mountains include types, such as calcitized flow rocks and hydro theImal dolomite, that are not present in the other areas, as well as argillized and silicified igneous and sedimentary rocks, which are common in the other study areas. Another important factor in the selection of this area is the presence of denser vegetation cover than is typical of most of the Basin and Range province. The pre-Tertiary stratigraphy of the East Tintic Mountains has been described in detail by Lindgren and Loughlin (1919), Morris (1957), and Morris and Lovering (1961), and the central part of the range is covered by 1:24,000 scale geologic maps of the Eureka quadrangle
,, 'ir.'. / ,, , ,t4, kr. ' .,1
/ SS ., , .., : Q Ts ' ( . 1
J --,iis? ;
' i' ik iNk0'''! 1 s - °‘,..' i ' Tss'1; , &PI
; ,/ i IS ', MI Tp
cu
i T 1 s , „ , , gx. .:
ri
l'. '''''t, OTS . '
, Too Tss 'N
, .000 .A.,... '
-; „
T Tpc 'v; cm ,cu
P
, OTs
, T ds:‘ 4"
'T1
.. A A' : Uli
:
CM-7f' , '.. 'Li '
i c!, /Cm.;;F„ ,, '- S6-UTP): 4'./AUX ' ,:?4 :. MAMMOTH _43 ,, ( to Eljs:RTETD(.:AmT4i: ''.. elkIt--c-mr . sc .‘Z.Ts , f ( Of IlkTINTIC
,? v i cm .c.,U / f . ..1.SC ... 1786 M lei 55' \-415 iys - 14/40 Tsc o? k 1.11/4 . fl,. ty-,, 4 - Tsci'.5 N Y. ' T S .:ScitivuERmc...z.: . cs: ' , v Ttm N? ' i l-Ttm 'Ll'. ‘.7 Ttm
sc.t .a. 0 4.f.s..J c. J--0--441psix.,,, ' (cr.' scLs.,urn nuBY !i.ifr ik,L.--1,LiNc..} 1.!,'"., ,,j 'SC
Tops
S , -2s, ..erki rr-- rn
y. /c 1./1 (v, ,r rs- , tm TSP1 Tsp ,--.0 s.A.r ,, Tim Ttm-c, (11's c.,,Ttm , it TspomiamOND 1.-; r 44.4 c-3 . — — q--Ttm Tim
J l'orTSpS C,!? i-, f3,M 1532 IA u}.- 6OTs „rt.: ,T t m -; ,„ TspP 0,Tsp Tsp t Ttm t rub Ts ps C/) CD o . cs-', itTli -r '11 6(4: h
'(Ttm -52:
e Lu) OTs 39 50'
ciTi.m\,,,,, , Tbp , ; Ns S-
/-) Tim ct? , Ts b h
0 Ts Tbh OTs Tbh
Ttm. e- Tsp) _rn 1‘).1, ,5 T 4 A441%
Figure 3 - Generalized geologic map of the study area (after. Morris and Mogensen, 1978). 2A
(Morris, 1964a), the Tintic Junction quadrangle (Morris, 1964b), and the Tintic Mountain quadrangle and the adjacent part of the McIntyre quad rangle (Morris, 1975). This discussion draws extensively from these works for lithologic descriptions of the sedimentary and igneous host rocks; however, because of- the low spatial resolution of the MSS images, reference is made mainly to the generalized 100,000 scale geologic map of the study area and a composite columar section shown in figure 3 and table 1, respectively (from Morris and Mogensen, 197S). A more detailed analysis is presented for the East Tintic mining district, however, because of the presence of a large variety of hydrothermal alteration products (Lovering, 1949). Particular attention is given to variations in surficial limonite content because of the common association of limonite with oxidized sulfide-bearing altered rocks and its diagnostic spectral reflectance in the MSS response range (Rowan and others, 1974; 1977). As used here, limonite consists mainly of hydrous iron-oxide minerals. Goethite is commonly dominant, but hematite and jarosite are also present; the individual mineral names are used where the components can be readily identified in the field. Spectral reflectance features at longer wave lengths are also considered, as these features may provide a basis for overcoming some of the limitations imposed by the MSS. No attempt has been made to evaluate the MSS images for structural information, even though north to north-northeast-trending faults were important in localizing ore minerals (Morris and Lovering, 1961) and some faults are quite apparent in the images.