Anomalies Of Cu Research Articles

Identification of Multi-Element Geochemical Anomalies for Cu–Polymetallic Deposits Through Staged Factor Analysis, Improved Fractal Density and Expected Value Function

Identification of Multi-Element Geochemical Anomalies for Cu–Polymetallic Deposits Through Staged Factor Analysis, Improved Fractal Density and Expected Value Function

Integration of geological and geophysical studies in order to mineral exploration at the Zaveh mineralization area, Khorasan Razavi Province, Iran

The copper deposit of Zaveh lies in the SE of the city of Torbat-e-Heydarieh and in middle of the Khaf-Kashmar-Bardaskan Magmatic Belt (KKBMB) in the Khorasan-e-Razavi Province. The lithology of the area consist of Jurassic and Cretaceous sedimentary rocks and Eocene volcanic units. Ore-formation is controlled by fault activity, representing vein-veinlet style E-W trending, formed within a conglomerate rich in quartz. Primary minerals are chalcopyrite, pyrite and arsenopyrite and secondary minerals contain malachite, azurite chalcocite, bornite, covellite, Cu sulphates, wad (Mn hydroxide), haematite, goethite, jarosite, limonite and (to a lesser extent) chrysocolla. The predominant alteration is silification which is associated with vein ore-formation. The volcanic units host propylitic, sericite, carbonate and silicification alterations. The ore-formation itself represents anomalies of Cu (2.1 % max), As (>1%), Sb (~105 gr/T), Pb (4371 gr/T) and Zn (1.1% max). Induced polarization and electrical resistivity (IP/RS) surveys unveil that the most chargeability anomaly corresponds to center of ore-forming vein and fault zone.The chargeability anomaly extends and amplifies with depth. The most amount of specific electrical resistance has been observed in the quartz-rich conglomerate. Interpretation of IP/RS data reveals that the chargeable source is extending in deeper beds (presumably sulphid ore-formation) which needs to be verified by boring operation. Geophysical surveys are significantly commensurate with field observations, ore-forming and geochemical data. Utilization Geophysical methods in different style of ore-deposits and interpretation of obtained information by means of geological, ore-forming and geochemistry data is considered to be a big step towards subterranean exploration and deposits modeling.

In situ major and trace element analysis of magnetite from carbonatite-related complexes: Implications for petrogenesis and ore genesis

Magnetite (Fe3O4) is one of the most common accessory minerals in magmatic rocks, and it can accommodate a wide variety of major, minor and trace elements that can be measured by laser ablation ICP-MS. In this study, we investigate the chemical compositions of magnetite from four carbonatite complexes (Oka, Mushgai Khudag, Hongcheon and Bayan Obo). The minor elements (Mg, Ti, Al, Mn) in magnetite vary significantly both within and between different complexes. High field strength elements (Zr, Hf, Nb, Ta, U, Th) are generally depleted in magnetite from carbonatite complexes, whereas K, Rb, Cs, Ca and P are commonly below detection limits. V and Zn display significant variations from tens to thousands of ppm. Co, Ni and Ga are present in ppm or tens of ppm, whereas Cu, Sr, Y, Ba and Pb are characterized by sub-ppm levels. Mo and Ge are identified at the ppm level, whereas a consistent concentration of 2–5 ppm is observed for Ge. The determined chemical compositions of magnetite from carbonatite complexes are quite distinguishable compared to those formed in silicate and sulfide melts. This is clearly shown using multielement variation diagrams, and the distinct signatures of carbonatite-related magnetite include strong positive anomalies of Mn and Zn and negative anomalies of Cu, Co and Ga. The discriminant diagrams of Ti vs. Zr + Hf, Ti vs. Nb + Ta and Ni/Cr vs. Ti are applicable for distinguishing magmatic and hydrothermal magnetite in carbonatite-related environments. In addition, the discriminant diagram of Zn/Co vs. Cu/Mo and Cu vs. Zr + Hf can be used to distinguish carbonatite-related magnetite from magnetite that formed in other environments.

Spatial distributions and the identification of ore-related anomalies of Cu across the boundary area of China and Mongolia

The 1:1, 000, 000 geochemical mapping across the boundary area of China and Mongolia has acquired high-quality basic geochemical data, yielding more than 9000 stream sediment samples and over 400 rock samples. Each stream sediment and rock sample site was assigned to the regional tectonic unit, geological background and geomorphic landscape maps, respectively, resulting in spatial data for three categorical variables. The contents and spatial distributions of Cu in stream sediment and rock samples across the boundary area of China and Mongolia were studied. The stream sediment geochemical data set was centered logratio transformed (clr) to avoid the closure effect. Random forest regression (RFR) was applied to predict Cu geochemical background for each sample with tectonic unit, geological background, and geomorphic landscape as characteristic variables, then the residuals were used to map geochemical anomalies. The study shows that Cu contents in stream sediments and rocks are high in the west and low in the east of the study area, and the median Cu varies with different tectonic units, geological backgrounds, and geomorphic landscapes. The background values of Cu are strongly spatial heterogeneous. The distributions of predicted Cu background values by random forest regression algorithm are similar to the distribution characteristics of Cu in stream sediments and rocks. The influence of tectonic units on the spatial variations of Cu geochemical background was greatest, followed by geological background, the influence of geomorphic landscape was smallest. The geochemical anomalies drawn by the residuals produced in random forest regression are in good agreement with the known deposits, indicating that the predicted geochemical background of Cu is reasonable and accurate, and has certain theoretical and practical significance.

Geochronological and geochemical constraints on the genesis of Cu-Au skarn deposits of the Santa María de la Paz district (Sierra del Fraile, Mexico)

Cu-Au skarn deposits of the mining district of Santa María de La Paz are located in the Sierra del Fraile, in the northern part of San Luis Potosí, Mexico. Samples of four different intrusions and their related skarn deposits were taken underground, in order to obtain whole-rock and mineral geochemical data. U-Pb LA-ICP-MS zircon data indicate crystallization ages of ca. 37.6–35.0 Ma for skarn-related granitic and granodioritic stocks, which show dominant metaluminous to slightly peraluminous, high-K calc-alkaline compositions. These intrusions were emplaced in a post-Laramide continental arc setting under shallow conditions, as suggested by fast cooling inferred from K-Ar biotite ages of ca. 35–33 Ma. Skarn deposits were contemporaneous with emplacement and crystallization of stocks, as revealed by Re-Os molybdenite geochronological data of exoskarn rocks. Skarn rocks show a general depletion of LILE and REE and a slightly enrichment in HFSE in comparison with intrusive rocks. Pyroxene and garnet show dominant hedenbergite and andradite compositions, respectively. The association of hedenbergite, pyrite, chalcopyrite, native bismuth and pyrrhotite during skarn mineralization suggest reducing conditions, typical for Au but not for Cu skarns. Highest metal contents are concentrated in exoskarn rocks, including anomalies of Cu, Fe, Ni, Sn, Sb, Zn, W and Bi. Metal contents, ore minerals and environmental conditions of skarn rocks, together with whole-rock geochemical data of stocks and pyroxene-garnet compositions, reveal some singularities for the Sierra del Fraile deposits, as they exhibit characteristics of both Cu and Au skarn deposits but might be also compatible with Fe, W, and Zn skarns. Hence, skarn and associated vein deposits of the Sierra del Fraile might have a high potential not only for Cu-Au, but also for several base metals, as reported for comparable post-Laramide skarn and hydrothermal deposits of central and northern Mexico.

Geochemical challenges of diverse regolith-covered terrains for mineral exploration in China

In recent years mineral exploration has concentrated on concealed deposits in regolith-covered terrains. In China, the regolith-covered landscapes mainly include desert windblown sand basins, desert peneplains, semi-arid grassland, loess plateaus, forestry land, alluvial plains and laterite terrains. These diverse regolith-covered areas represent geochemical challenges for mineral exploration in China. This paper provides an overview of recent progress on mechanisms of metal dispersion from the buried ore deposits through the transported cover to the surface and penetrating geochemical methods to detect the anomalies. Case studies show that, in arid and semi-arid desert sand-covered terrains, sampling of fine-fraction (−120mesh, <0.125mm) clay-rich horizon soil is cost-effective for regional geochemical surveys for sandstone-type uranium, gold, and base metal deposits. Fine-fraction sampling, selective-leaching and overburden drilling geochemical methods can effectively indicate the 210 gold ore body at Jinwozi goldfield. In alluvium-covered terrains, fine-grained soil sampling (−200mesh, <0.074mm) combined with selective leaching geochemistry shows clear ring-shaped anomalies of Cu and Ni over the Zhouan concealed Cu–Ni deposit. In laterite-covered terrains, the anomalies determined by the fine-fraction soils and selective leaching of absorbed metals on coatings of Fe–Mn oxides coincide well with the concealed deposit over the Yueyang ore deposits at the Zijin Au–Cu–Ag field. Nanoparticles of hexagonal crystals mainly native copper, gold and alloys of Cu–Fe, Cu–Fe–Mn, Cu–Ti, and Cu–Au were observed in gases, soils and ores using a transmission electron microscope (TEM). The findings imply that nanoparticles of gold and copper may migrate through the transported cover to the surface. Uranium is converted to uranyl ions [UO22+] under oxidizing conditions when migrating from ore bodies to the surface. The uranyl ions are absorbed on clay minerals, because clay layers have a net negative charge, which needs to be balanced by interlayer cations. Nanoparticles of Au and Cu and ion complexes of U are more readily absorbed onto fine fractions of soils containing clays, colloids, oxides and organic matters. Thus, fine-grained soils enriched with clays, oxides and colloids are useful media for regional geochemical surveys in regolith-covered terrains and in sedimentary basins. Fine-fraction soil sampling combined with selective leaching geochemistry is effective for finding concealed ore bodies in detailed surveys. Penetrating geochemistry at surface sampling provides cost-effective mineral exploration methods for delineation of regional and local targets in transported cover terrains.

A Fast Independent Component Analysis Algorithm for Geochemical Anomaly Detection and Its Application to Soil Geochemistry Data Processing

A fast independent component analysis algorithm (FICAA) is introduced to process geochemical data for anomaly detection. In geochemical data processing, the geological significance of separated geochemical elements must be explicit. This requires that correlation coefficients be used to overcome the limitation of indeterminacy for the sequences of decomposed signals by the FICAA, so that the sequences of the decomposed signals can be correctly reflected. Meanwhile, the problem of indeterminacy in the scaling of the decomposed signals by the FICAA can be solved by the cumulative frequency method (CFM). To classify surface geochemical samples into true anomalies and false anomalies, assays of the 1 : 10 000 soil geochemical data in the area of Dachaidan in the Qinghai province of China are processed. The CFM and FICAA are used to detect the anomalies of Cu and Au. The results of this research demonstrate that the FICAA can demultiplex the mixed signals and achieve results similar to actual mineralization when 85%, 95%, and 98% are chosen as three levels of anomaly delineation. However, the traditional CFM failed to produce realistic results and has no significant use for prospecting indication. It is shown that application of the FICAA to geochemical data processing is effective.

Delineation of geochemical anomalies using factor analysis and multifractal modeling based on stream sediments data in Sarajeh 1:100,000 sheet, Central Iran

The aim of this study is to delineate the Cu, Au, and Pb anomalies in Sarajeh 1:100,000 sheet located in Urumieh-Dokhtar ore belt, central Iran. The analyzed elements of stream sediment samples taken in the area can be classified into six groups (factors) by factor analysis. The concentration–area and number–size multifractal inverse distance weighted models were applied for recognition of the elemental thresholds which are similar in both used multifractal models. According to the thresholds, the elemental concentration distribution for Cu, Au, and Pb were divided to three lithological classifications, namely mainly c alkaline porphyry with Cu–Au mineralization, mafic and sedimentary rocks. The results illustrate that the major anomalies of Cu, Au, Pb and related factors are mostly located around intrusions, volcanics, and along NW–SE faults.

COMPILATION OF GEOLOGY, MINERALIZATION, GEOCHEMISTRY AND GEOPHYSICAL STUDY OF IP/RS & GROUND MAGNETIC SURVEY AT ROUDGAZ AREA, SOUTHEAST OF GONABAD, KHORASAN RAZAVI PROVINCE

منطقه اکتشافی رودگز، یک سیستم پلی متال مس، قلع، سرب، روی و طلای رگه ای است که در جنوب‌شرق گناباد و شمال‌شرق بلوک لوت قرار دارد. توده های نفوذی نیمه عمیق ترشیری با ترکیب مونزونیت تا مونزودیوریت پورفیری نوع اکسیدان در سنگهای دگرگونی به سن ژوراسیک میانی نفوذ نموده اند. اغلب توده های نفوذی تحت تأثیر آلتراسیون های کربناتی، آرژیلیک، سریسیتی و سیلیسی- تورمالینی قرار گرفته اند. کانی سازی در منطقه، کنترل گسلی داشته و به‌صورت رگه ای با روند عمدتا NW-SE و شیب 85 تا 90 درجه وجود دارد. کانیهای اولیه شامل کوارتز، تورمالین، کالکوپیریت، پیریت و کانیهای ثانویه مالاکیت، آزوریت و گوتیت است. نمونه برداری ژئوشیمیایی به روش خرده سنگی، ناهنجاریهای بالایی (تا ppm 10000) از عناصر مس، قلع، سرب و آرسنیک، روی (تا ppm5527) و طلا (تا ppb 325) را نشان می دهد. زون گوسان وسیع در منطقه وجود دارد که در ارتباط با اکسید شدن کانیهای سولفیدی است. برداشتهای IP/RS به‌منظور تعیین موقعیت و گسترش کانی سازی سولفیدی در عمق بر روی ناهنجارهای ژئوشیمی انجام شد. به‌طورکلی، در محل زون های گوسان، رگه ها، کنده کاریهای قدیمی و در محل ناهنجاریهای ژئوشیمی، شارژابیلیته افزایش می یابد. مقاومت ویژه بر روی واحد کوارتزیت و همچنین در مکانهایی که رگه کانی‌سازی با کوارتز همراه است، ناهنجاری بالا تا 425 اهم‌متر دارد. به‌دلیل ناهنجاری بالای ژئوشیمیایی عنصر قلع و ارتباط آن با توده های نفوذی احیایی، برداشتهای مغناطیس‌سنجی -زمینی به‌منظور شناسایی موقعیت توده های سری مگنتیت (اکسیدان) و ایلمنیت (احیایی) در عمق انجام شد. تغییرات شدت کل میدان مغناطیسی در نقشه TMI به میزان 1/335 گاما است. بالاترین ناهنجاری مغناطیسی در نقشه RTP در شمال منطقه برداشت قرار دارد که مرتبط با توده های سری مگنتیت (هورنبلند بیوتیت مونزودیوریت پورفیری) بوده و در عمق به‌سمت جنوب گسترش دارد. کمترین ناهنجاری مغناطیسی در مرکز محدوده (شرق روستای رودگز) قرار دارد که با محل بیشترین مقادیر ناهنجاری شارژابیلیته و ژئوشیمی منطبق است. براساس ناهنجاری ژئوشیمی و شارژابیلیته، دو گمانه در محل حفاری و 24 نمونه ژئوشیمیایی از مغزه ها برداشت گردید که بیشترین ناهنجاریها همراه با آلتراسیون سیلیسی- کلریتی و مناطق با گسترش اکسیدهای آهن ثانویه است.

Geochemistry of stream sediments southwards of the SW Variscan suture in Portugal (Guadiana and Chança river basins): insights into element anomalies of variable origin and intensity

Stream sediment samples were collected in the Trindade–Chança region at 1034 sites for mineral exploration purposes during 1996–97. Concentrations of Cu, Zn, Pb, Co, Cr and Ni are high enough in most sample sites to allow data assessment by multi-element anomaly definition and threshold computation using the area concentration multifractal model technique. The regional threshold values are 20, 45, 30 and 15 ppm for Cu, Zn, Pb and Co respectively. Anomalies for Cu, Zn, Pb, Co, Cr and Ni are delimited by first order local threshold values at 40, 94, 70, 21, 37 and 42 ppm. The main anomalies are clustered to the east-southeast of the surveyed region and reflect mixed contributions from a variety of sources, namely different volcanic units with local contributions from pelite rocks, contamination from old (abandoned) mining activities and hydrothermal mineralisation controlled by different fault zones.

Identifying geochemical anomalies associated with Cu and Pb–Zn skarn mineralization using principal component analysis and spectrum–area fractal modeling in the Gangdese Belt, Tibet (China)

The Gangdese Belt is now recognized as an important Cu polymetallic mineralization belt. Recent studies suggest that apart from porphyry copper deposits, polymetallic skarn deposits are another significant deposit type in this belt. In this paper, principal component analysis (PCA) and spectrum–area ( S– A) fractal modeling are used to identify geochemical anomalies associated with Cu and Pb–Zn skarn mineralization based on Cu, Pb, Zn and Ag stream sediment data. Firstly, the raster maps of Cu, Pb, Zn and Ag were obtained by multifractal inverse distance weighted (MIDW). Secondly, PCA was used to combine the Cu, Pb, Zn and Ag concentration values. Finally, S– A analysis was used to decompose the first component pattern obtained by the PCA. The results show that major anomalies of Cu, Pb, Zn and Ag are mostly located around mapped intrusions, and along E–W trending faults, where Cu and Pb–Zn skarn deposits favorably occur. These results indicate that: (1) the Gangdese Belt potentially hosts undiscovered Cu and Pb–Zn skarn deposits, and the integrated anomalies for Cu, Pb, Zn and Ag occurring around the intrusions and in the vicinity of faults in the center part of the Gangdese Belt should be further investigated in the next step of mineral resource exploration; and (2) the hybrid method combining PCA and S– A modeling is an effective tool to identify geochemical anomalies.

Application of singularity mapping technique to identify local anomalies using stream sediment geochemical data, a case study from Gangdese, Tibet, western China

Identifying geochemical anomalies from background is a fundamental task in exploration geochemistry. The Gangdese mineral district in western China has complex geochemical surface expression due to complex geological background and was chosen as a study area for recognition of the spatial distribution of geochemical elements and separating anomalies from background using stream sediment geochemical data. The results illustrate that weak anomalies are hidden within the strong variance of background and are not well identified by means of inverse distance weighted; neither are they clearly identified by the C–A method if this method is applied to the whole study area. On the other hand, singularity values provide new information that complements use of original concentration values and can quantify the properties of enrichment and depletion caused by mineralization. In general, producing maps of singularities can help to identify relatively weak metal concentration anomalies in complex geological regions. Application of singularity mapping technique in Gangdese district shows local anomalies of Cu are not only directly associated with known deposits in the central part of the study area, but also with E–W and N–E oriented faults in the north of the study area. Both types of anomalies should be further investigated for undiscovered Cu mineral deposits.

Mineral deposits and Cu–Zn–As dispersion–contamination in stream sediments from the semiarid Coquimbo Region, Chile

This paper presents Cu–Zn–As geochemical data from stream sediment surveys carried out in the three main watersheds of the Coquimbo Region of Chile. This mountainous semiarid realm occupies an area of 40,656 km2 between 29° and 32°S. Given that the area has a long historical record of mining activities, important environmental disturbances were expected. However, despite the detection of three major geochemical anomalies for Cu, Zn, or As, only one can be unmistakably linked to the development of mining–metal recovery procedures (Andacollo–Panulcillo). An investigation of the other two anomalies (Elqui and Hurtado) reveals three major causes that fully or partially account for them: (1) the type of ore deposit and associated hydrothermal alteration; (2) the regional structural setting (intensity of fracturing); and (3) climate–landscape. Cu–Au–As epithermal deposits/prospects along the so-called El Indio belt are here regarded as the sources of both the Elqui and Hurtado anomalies. The strong advanced argillic alteration present in some of the epithermal deposits/prospects of the El Indio belt may have induced the loss of the buffering capacity of rocks, and therefore favoured metal dispersion during later oxidation–leaching of sulphides. This applies to the Elqui and Hurtado anomalies. Conversely, given that the potassic, propylitic and phyllic alterations do not affect the buffering capacity of rocks, only minor metal dispersion is observed in relation to the Los Pelambres porphyry copper deposit. Besides, the epithermal belt is located within a highly fractured Andean domain (3,000–4,000 m of altitude), which may have conditioned the fast unroofing of ore deposits, contributed to enhanced circulation of meteoric waters, and eventually, to strong oxidation, and leaching of metals. Metal dispersion is aggravated during rainy years in response to strong El Niño episodes.

Endeavour 26 North; a porphyry copper-gold deposit in the Late Ordovician, shoshonitic Goonumbla volcanic complex, New South Wales, Australia

Endeavour 26 North is the largest of 12 pipelike porphyry Cu-Au deposits found near Parkes in central- west New South Wales, within the Late Ordovician Goonumbla Volcanic Complex. The dominant volcanic rocks of the complex, the Goonumbla Volcanics, are latitic flows and volcanic breccias which are overlain by the trachytic Wombin Volcanics. The volcanic rocks are characterized by high K 2 O and high K 2 O/Na 2 O ratios, which are typical of the shoshonite association, as well as an enrichment in large ion lithophile elements and a low concentration of high field strength elements. The Nelungaloo Volcanics form an Early Ordovician, nonshoshonitic volcanic substrate to the complex which initially developed in a submarine and subsequently subaerial setting. The 87 Sr/ 66 Sr, epsilon Nd , and Pb isotope data indicate the magmas were derived from mantle sources. The shoshonitic magmas may be products of high-pressure fractionation in the subcontinental lithosphere. The porphyry deposits are associated with a gravity low which is taken to reflect a subvolcanic chamber beneath the center of the complex. All deposits are located within a pronounced circular feature in the aeromagnetic data that is interpreted as the margin of a collapsed caldera. Dioritic to monzonitic stocks, which in part define the caldera rim, represent a resurgent phase of magmatism. The Endeavour 31 stock which was part of this phase is ringed by six porphyry Cu-Au deposits, including Endeavour 26 North. The deposits are centered on fingerlike quartz monzonite porphyries which cut the Endeavour 31 stock at depth. Geochemical anomalies of Cu and Zn in the bedrock define the size of the alteration system associated with the stock. In part the distribution of the Cu-Au deposits is controlled by the Endeavour lineament. In comparison to most other volcanic and intrusive rocks of the Goonumbla Volcanic Complex, the Endeavour..

The use of “loam” concentrates in geochemical exploration in deeply weathered arid terrains

This paper reviews some aspects of the use of “loam” (soil) concentrates in geochemical surveys in arid, deeply weathered environments. An orientation survey at a small Ni-Cu-Co prospect in Western Australia has shown that discrimination between mineralized and unmineralized samples could be achieved using Ni, Cu, Co, Cr, Zn, As, Sn, Sc, Ti, Yb and Y in the coarse fraction of heavy concentrates. However, at the same prospect the best contrast for Ni, Cu and Co in surface samples was provided by analysis of the same fraction following a cold ammonium citrate/hydroxylamine hydrochloride digestion. At a nearby, larger prospect, some 54 km2 in area, concentrates were separated, by jigging, from bulk soil samples, themselves composites of representative subsamples. Sampling at a density of 4 samples per km2 revealed 1–2 km2 size anomalies of Cu, Ni, Co, Cr, As and Au which could be related, variously, to known Ni-Cu and Au mineralization. In Botswana, analysis of concentrates, separated by tabling from samples collected at a density of 1 sample per 7.5 km2 over an area of 5400 km2, identified distinctive geochemical districts. Enhanced values of Au and of Cu-Ni in the concentrates were relatable to known mineralization and the results suggested that there were also Sn-W-Mo-Bi (granitoid) and Au-Pb-Zn-Bi-Sn (volcanogenic) associations which could lead to new prospecting targets. Anomalies of certain elements (for example, Cu in an ultramafic environment) may be more readily detected in surface material by “enrichment indexing” the concentrate data.

Distinguishing significant from false copper and nickel anomalies in soil overlying the Gladesville norite, Jasper County, Georgia

Abstract Distinct anomalies of Cu and Ni in stream alluvium and soil are associated with the Gladesville norite, but are generally not related to significant mineralization. The origin of one of the soil anomalies was investigated by determining partitioning relationships of Cu and Ni in outcrop samples, B-horizon soil samples, and a soil profile sample utilizing selective leaching techniques and electron microprobe analyses. Silicate minerals and spinel are important controls of both Cu and Ni distribution in the outcrop samples. Sulfides are a minor residence site of Ni but an important residence site of Cu. In soil, scavenging of Cu by montmorillonite has been important. Disintegration of montmorillonite in the B-horizon leaves residual minerals as an important and probably dominant control of Cu distribution in the upper part of the soil. Iron oxide particle coatings contain more Ni (46%) than any other single material in the B-horizon soil samples but contain only 21% of the Cu. Certain characteristics of the investigated Cu and Ni soil anomaly may be significant in future exploration as indicators of “false” anomalies. These include areal anomaly distribution patterns, soil/bedrock metal ratios, and the tendency of each metal to reside principally in a single soil component.