Conceptual models in exploration geochemistry: The Canadian Cordillera and Canadian Shield

This volume summarizes the exploration geochemical conditions in the secondary environment, in the Canadian Cordillera and the Canadian Shield. This is achieved by a number of conceptual models which describe the principles and mechanisms of formation of anomalies, which govern the use of exploration geochemistry. These models have been constructed by drawing together information already existing in the literature plus 38 individual case histories contained in this volume.The formation of anomalies is described for: (1) residual overburden, (2) overburden of local origin (e.g. till), and (3) transported overburden of remote origin (e.g. stratified glacial drift and alluvium). Within each of these categories the effect of element mobility, seepage zones, bogs, variation in overburden thickness, rock type change and soil type change are also described.An attempt has been made, not only to summarize both these conditions where geochemistry can be used as a reliable exploration tool, but also to identify areas where the use of geochemistry is unreliable.A summary is also given of the length of anomalous dispersion and contrast in both soil and sediments for all the case histories quoted, both in this volume and in the literature. This summary is divided according to the type of deposit, i.e. porphyry copper, massive sulphide, etc., and provides a guide for planning the optimum sampling interval.     

Receiver operating characteristics (ROC) as validation tool for prospectivity models — A magmatic Ni–Cu case study from the Central Lapland Greenstone Belt,Northern Finland

A prospectivity model for magmatic Ni–Cu deposits was created by integrating spatially referenced geophysical and geochemical datasets based on a simple and practical exploration model. The study area is the Central Lapland Greenstone Belt, Northern Fennoscandian Shield, Finland. Magmatic nickel deposits are related to rock types that are typically characterized by local magnetic and gravity anomalies. These deposit types can also be a source of nickel, copper and cobalt anomalies in the overlying glacial till cover. This straightforward exploration criterion was translated into a fuzzy logic prospectivity model. The model validation is an essential step in justifying the validity of the prospectivity model. This was accomplished by using receiver operating characteristics (ROC) technique. We used the known Ni–Cu occurrences and deposits as true positive cases and other deposit type locations or random points as true negative cases in the validation process. It appears that the ROC technique provides a robust model validation and optimization technique, providing that suitable validation data exists.     

Glacial geology as a key to geochemical exploration in areas of glacial overburden with particular reference to Canada

The applicability of geochemical exploration procedures in previously glaciated areas is largely a function of the nature of the glacial sediments. A considerable diversity of glacial sediments and landforms results from a phase of glaciation, these products bearing variable compositional relationships to the local bedrock, and thus have varying usefulness in geochemical exploration. A classification of glacial sediments and landforms is described, with emphasis being placed on the provenance of the material composing the different types. The nature and extent of the Wisconsin glaciation in Canada is summarized, together with a review of the distribution of glacial sediments and landforms. Variations in the nature of the glaciation and the distribution of different glacial sediments and landforms have contributed to the situation that the applicability of geochemical exploration techniques varies across Canada. The nature of metal dispersion in glacial sediments resulting directly from glacial activity is discussed, particular reference being given to those features that have proved effective in geochemical exploration. The role of dispersion patterns in glacial sediments and landforms is discussed with regard to varying scales of geochemical exploration programs. Variations in the distribution of glacial sediments and the nature of associated dispersion patterns, both on the regional and local scales, make a consideration of the glacial geology an essential feature for the implementation of appropriate geochemical exploration procedures.     

Regional subglacial quarrying and abrasion below hard-bedded palaeo-ice streams crossing the Shield–Palaeozoic boundary of central Canada: the importance of substrate control

Three-dimensional surface visualization models derived from high-resolution LiDAR data provide new information about the type and scale of erosional processes below Late Wisconsin palaeo-ice streams traversing the boundary between Canadian Shield crystalline rocks with offlapping Palaeozoic limestones in central Ontario. The hard bed is directly analogous to that found below ice streams in East Antarctica and East Greenland and provides insight into the effects of abrupt changes in substrate type on subglacial processes. Erosion of hard crystalline Canadian Shield rock was largely ineffectual consisting of areal abrasion of rounded whalebacks and local lee side plucking. In contrast, fast flow over the strike of gently dipping well-bedded and jointed Palaeozoic limestones cut large flow-parallel grooves and ridges akin to mega-scale glacial lineations reflecting intense abrasion below narrow streams of subglacial debris dominated by hard crystalline Shield clasts (erodents). Regionally extensive plucking of structurally weak, well-jointed and bedded limestone produced large volumes of rubbly carbonate debris leaving a 25-km-wide belt of uncontrolled hummocky rubble terrain (long known as the Dummer Moraine in Southern Ontario) some 350 km long and locally as much as 10 m thick. Subglacial plucking and abrasion under fast flowing ice were highly effective in stripping limestone cover rocks from Precambrian basement, and over many glacial cycles, may have played a role in the location and excavation of numerous large and deep lake basins around the Shield–Palaeozoic boundary zone in North America.     

Influence of the Laurentide Ice Sheet and relative sea‐level changes on sediment dynamics in the Estuary and Gulf of St. Lawrence since the last deglaciation

Physical properties, grain size, bulk mineralogy, elemental geochemistry and magnetic parameters of three sediment piston cores recovered in the Laurentian Channel from its head to its mouth were investigated to reconstruct changes in detrital sediment provenance and transport related to climate variability since the last deglaciation. The comparison of the detrital proxies indicates the succession of two sedimentary regimes in the Estuary and Gulf of St. Lawrence (EGSL) during the Holocene, which are associated with the melting history of the Laurentide Ice Sheet (LIS) and relative sea‐level changes. During the early Holocene (10–8.5 cal. ka BP), high sedimentation rates together with mineralogical, geochemical and magnetic signatures indicate that sedimentation in the EGSL was mainly controlled by meltwater discharges from the local retreat of the southeastern margin of the LIS on the Canadian Shield. At this time, sediment‐laden meltwater plumes caused the accumulation of fine‐grained sediments in the ice‐distal zones. Since the mid‐Holocene, postglacial movements of the continental crust, related to the withdrawal of the LIS (c. 6 cal. ka BP), have triggered significant variations in relative sea level (RSL) in the EGSL. The significant correlation between the RSL curves and the mineralogical, geochemical, magnetic and grain‐size data suggest that the RSL was the dominant force acting on the sedimentary dynamics of the EGSL during the mid‐to‐late Holocene. Beyond 6 cal. ka BP, characteristic mineralogical, geochemical, magnetic signatures and diffuse spectral reflectance data suggest that the Canadian Maritime Provinces and western Newfoundland coast are the primary sources for detrital sediments in the Gulf of St. Lawrence, with the Canadian Shield acting as a secondary source. Conversely, in the lower St. Lawrence Estuary, detrital sediments are mainly supplied by the Canadian Shield province. Finally, our results suggest that the modern sedimentation regime in the EGSL was established during the mid‐Holocene.     

Regional geochemical anomalies related to plate tectonic models for the Northwestern Canadian shield

Regional geochemical maps of a 97,000-km² area of the northwestern Canadian Shield were based on analysis of lake sediment samples collected at 5-km grid points. The maps revealed three global-scale geochemical features: (1) a major anomaly of refractory and chalcophile elements associated with a Proterozoic volcanic-plutonic belt of previously proposed Andean are affinities; (2) a dramatic increase in Ba concentrations on crossing a proposed Precambrian suture zone; and (3) another major anomaly of refractory and chalcophile elements associated with the Archean greenstone belt closest to the supposed suture zone.The regional geochemical anomaly in the Proterozoic volcanic-plutonic belt is considered to have originated during an island-arc-type evolution of the belt by intrusion of magma formed by stages of partial melting of subducted oceanic basalts contaminated by subducted ocean floor sediments. The increase in Ba concentration found on crossing the proposed Precambrian suture is attributed to exposure of deep crust by the post-collision erosion of the uplifted edge of one of the proto-continents. The multielement, geochemical signature of the Archean greenstone belt is tentatively attributed to Archean subduction of oceanic crust and ocean sediments.The regional, multielement anomalies delineated are associated with known or suspected base metal and uranium mineralization. If the geotectonic relationships proposed above are valid, routine geochemical mapping of the Precambrian Canadian Shield will not only be of use in prospecting and mineral potential evaluation but may indirectly assist in metallogenic interpretations. Further, there is a possibility that routine geochemical mapping of the Canadian Shield may define other subduction and suture zones.     

Till geochemical and indicator mineral methods in mineral exploration

This paper summarizes advances since 1987 in the application of glacial sediment sampling to mineral exploration (drift prospecting) in areas affected by continental or alpine glaciation. In these exploration programs, clastic glacial sediments are tested by geochemical or mineralogical methods to detect dispersal trains of mineral deposit indicators that have been glacially transported from source by mechanical processes. In glaciated terrain the key sampling medium, till, is produced by abrasion, crushing and blending of rock debris and recycled sediment followed by down-ice dispersal ranging from a few metres to many kilometres. As a consequence of the mid-1980s boom in gold exploration, the majority of case studies and regional till geochemical surveys published in the past decade deal with this commodity. Approximately 30% of Canada and virtually all of Fennoscandia have been covered by regional till geochemical surveys that aid mineral exploration and provide baseline data for environmental, agricultural, and landuse planning. The most profound event in drift prospecting in the last decade, however, has been the early-1990s explosion in diamond exploration which has dramatically increased the profile of glacial geology and glacial sediment sampling and stimulated changes in sampling and analytical methods.     

Some conceptual models for geochemistry in areas of preglacial deep weathering

In some glaciated regions, weathered mantles, formed under previous climatic regimes, were not always eroded bare by glacial activity, but instead lie buried beneath the glacial overburden. It is obviously important that geochemical exploration programs in such terrain should take into account some of the known regolith features seen in deeply weathered regions. The effects of glacial action upon deeply weathered terrain are considered in three conceptual models. The critical factor in each is the depth of truncation of the preglacial weathering profile. All three proposed models are dynamic systems and a wide range of intermediate situations must be expected.In Model 1 a complete, largely undisturbed, weathering profile is preserved beneath till. The key characteristic is preservation of a lateritic duricrust which may contain areally large (up to 200 km²) geochemical anomalies. It would be critical, firstly, that the duricrust be sufficiently continuous to allow a reasonable success rate in its being sampled, and secondly that the duricrust be recognizable in drill spoil. The most efficient geochemical exploration could be based upon wide-spaced overburden drilling directed at sampling the duricrust. For reconnaissance, holes could be based upon a 1-km grid where stratabound massive polymetallic sulphide or stratabound gold deposits are sought. Even wider spacing could be tried where larger-sized ore deposits are expected.Model 2 is characterized by a weathered profile that was partly stripped prior to glaciation. The essential feature is a vertically zoned weathering profile in the basement rock in which the upper levels of the weathering profile have undergone leaching of certain elements and lower levels contain enrichments of these elements. Any gossans present would show strong vertical zonation. Relatively strong sources for dispersion in till are likely to be enriched gossans where erosion has cut deep into the profile, zones of supergene enrichment of ore deposits, and supergene ore deposits themselves. In many situations, saprolite under glacial drift would be too soft to provide boulders so important in conventional till prospecting.The essential ingredient in hypothetical Model 3 involves progressive planing away of the weathering profile by glacial action. Thus any halo in duricrust is initially dispersed, followed by dispersion of progressively deeper levels of saprolite. If taken deep enough the supergene enriched zone of a mineral deposit could add to the glacial dispersion. A broadly zoned anomaly would be expected; a till anomaly would be characterized distally by elements from the former duricrust anomaly, with elements more characteristic of supergene zones closer to the source.     

Water-rock interaction and chemistry of groundwaters from the Canadian Shield

The chemical and isotopic compositions of groundwaters in the crystalline rocks of the Canadian Shield reflect different degrees of rock-water interactions. The chemistry of the shallow, geochemically immature groundwaters and especially of the major cations is controlled by local rock compositions, whereby dissolution reactions dominate. Conservative constituents, such as chloride and bromide, however, are not entirely a result of such reactions but appear to be readily added from leachable salts during the initial stages of the geochemical evolution of these waters. Their concentration changes little as major cations increase, until concentrations of Total Dissolved Solids (TDS) reach 3000 to 5000 mg 1^?1. The isotopic composition of these shallow waters reflects local, present day precipitations.In contrast to the shallow groundwaters, the isotopic and chemical compositions of the deep, saline waters and brines are determined by extensive, low-temperature rock-water interactions. This is documented in major ion chemistries, ¹⁸O contents and strontium isotopic compositions. These data indicate that the deep brines have been contained in hydrologically isolated “pockets”. The almost total loss of primary compositions make discussions on the origin of these brines very speculative. However, all brines from across the Canadian Shield have a very similar chemical composition, which probably reflects a common geochemical history. The concentrations of some major and most minor elements in these fluids appear to be governed by reactions with secondary mineral assemblages.     

Palaeo-ice streams and the subglacial landscape mosaic of the North American mid-continental prairies

The analysis of the glacial landscape of southern Saskatchewan (Canada) through multiple data sets (e.g. digital elevation model, till compositional data) has revealed previously unrecognized subglacial sediment–landform assemblages. A southwest-trending corridor of mega-scale till lineations (Maskwa corridor) bounded on each side by hummocky terrain extends from the Canadian Shield to southwestern Saskatchewan. This landform assemblage is clearly cross-cut by a broad south to southeast trending corridor (Buffalo corridor) consisting of subparallel curvilinear till ridges. The carbonate content of the surface till is spatially consistent within these assemblages, suggesting a strong sediment–landform relationship. The two corridors are interpreted as the product of palaeo-ice streams. The Maskwa palaeo-ice stream flowed up the regional slope and across preglacial valleys, indicating it was thick and stable. Narrow dispersal trains extending across as well as down-glacier from the Athabasca Basin suggest that the Maskwa palaeo-ice stream extended far into the ice sheet across contrasting shield and platform terrains. In comparison, the Buffalo palaeo-ice stream was thinner and largely controlled by subglacial geology and topography. Its catchments were located at the Canadian Shield boundary and the system was oriented along-slope. It experienced lateral shifts and it was fed by a network of tributaries. The glacial dynamics shift from the Maskwa to the Buffalo system occurred at about 13.5 ¹⁴C kyr BP. The Buffalo system later evolved into thin outlet lobes until final deglaciation of the area. The proposed model has implications for ice-sheet reconstruction and the assessment of till properties in the prairies and in similar terrains.     

A Method for Eliminating Caprock Thickness Influence on Anomaly Intensities in Geochemical Surface Survey for Hydrocarbons

All petroliferous basins exhibit near-surface anomalous signals. The successful use of these signals must lead to great development in petroleum exploration. However, oil/gas fields cannot be effectively predicted in the case of intensive influence of caprock thickness on intensities of anomalies in a geochemical survey for hydrocarbons. In this paper, we first study the features of the influence of caprock thickness and then establish digital conceptual models for the influence in one and two dimensions. Finally, we develop techniques for eliminating this influence with wavelet analysis, based on the digital conceptual models. The newly developed techniques are applied to the actual data of acid-extractable hydrocarbons of soils in the southern slope of the Dongying Depression, East China where the anomaly intensities are considerably influenced by caprock thickness. The results illustrate that this new approach enables us to satisfactorily eliminate the influence of caprock thickness on anomaly intensities and thus can greatly improve the predictive capability of the existing geochemical data.     

Biogeochemical indicators of buried mineralization under cover,Talbot VMS Cu–Zn prospect,Manitoba

Results are presented of a surficial geomicrobiological investigation of glacial cover overlying buried mineralization at the Talbot prospect, Manitoba, Canada, where previous surficial geochemistry surveys indicated anomalous concentrations of elements above the buried mineralization. The Cu–Zn volcanogenic massive sulfide (VMS) occurrence is overlain by 100 m of Paleozoic dolomites and Quaternary glacial cover. The geomicrobiological investigation demonstrates that there is a distinct microbial ecology at the anomalous sampling locations, especially directly overlying buried mineralization. The combined geochemical and geomicrobiological analyses reveal the presence of an anomaly directly over mineralization due to oxidation of the buried ore. Specifically, geomicrobiological analyses yield an inverse correlation between Zn in the clay-size (<2 μm) fraction and total microbial biomass and a direct correlation between Cu in the clay-size (<2 μm) fraction and abundance of methanotrophic bacteria. These results demonstrate that microbiological analyses can be a useful addition to geochemical exploration by revealing metal transport and sequestration processes and enhancing surficial anomalies.     

2011~2020年勘查地球化学数据处理研究进展

我国建立了包含海量数据的高质量的勘查地球化学数据库,为矿产勘查、环境评价和地质调查等提供了重要的数据支撑。如何高效处理勘查地球化学数据,并从中发掘和识别深层次信息一直是勘查地球化学学科研究的热点和前沿领域。本文在系统调研国内外学者过去十年发表的论著基础上,对勘查地球化学数据处理方法进行分析与对比,从勘查地球化学数据库建设、地球化学异常识别及其不确定性评价等方面概述了我国近十年来在该领域取得的主要研究进展,包括:(1)分形与多重分形模型由于考虑了地球化学空间模式的复杂性和尺度不变性,在全球范围内得到极大的发展和推广,我国学者引领了基于分形与多重分形的勘查地球化学数据处理;(2)机器学习和大数据思维开始在该领域启蒙,并迅速得到关注,正在成为研究热点和前沿领域,我国学者率先开展基于机器学习算法的勘查地球化学大数据挖掘研究;(3)我国学者需要进一步加强勘查地球化学数据缺失值处理以及成分数据闭合效应研究。今后该领域应进一步加强对弱缓地球化学异常识别、异常不确定性评价以及异常识别与其形成机理相结合等方面的研究。     

中国主要类型铜矿勘查地球化学模型

本文是《中国主要类型铜矿隐伏矿地球化学预测指标研究》项目成果的综述。该项目以我国40多个铜矿床不同级次的地质、地球化学资料为基础,研究了斑岩型、夕卡岩型、复合型、岩浆型、海相火山岩型、沉积变质—热液改造型和热液脉型铜矿的矿带、矿田、矿床地球化学特征,总结了各矿床的地球化学异常模式,建立了各铜矿类型的勘查地球化学模式—模型系统。     

Multipurpose geochemical maps produced by integration of geochemical exploration data sets in The Paraná Shield, Brazil

Old geochemical datasets from the Paraná Shield of southern Brazil have been integrated into a new geochemical database and the results are presented as a series of multipurpose geochemical maps. Although the 24 datasets retrieved were analysed by three different laboratories, the maps produced correlate surprisingly well with bedrock geological features.The retrieval of old geochemical exploration data sets for the purpose of generating maps showing element depletions and enrichments is a powerful tool with a wide range of applications: trace elements such as Zn, Cu and Mo can significantly affect crop productivity; areas with high abundances of harmful elements such as As and F can be delineated in order to identify public health hazards; heavy metals such as Cd, Pb and Hg can be measured in order to better constrain knowledge of chemical background levels for environmental monitoring. The integration and manipulation of different data sets can however be complicated by the heterogeneity in sampling and analytical procedures.     

A chlorine-36 study of regional groundwater flow and vertical transport in southern Nevada

Chlorine-36 data for groundwater from the Death Valley regional flow system is interpreted in the context of existing conceptual models for regional groundwater flow in southern Nevada. Chlorine-36 end member compositions are defined for both recharge and chemically evolved groundwater components. The geochemical evolution of ³⁶Cl is strongly controlled by water-rock interaction with Paleozoic carbonate rocks that comprise the regional aquifer system, resulting in chemically evolved groundwater that is characteristically low in ³⁶Cl/Cl and high in Cl. Groundwater from alluvial and volcanic aquifers that overlie the regional carbonate aquifer are generally characterized by high ³⁶Cl/Cl and low Cl signatures, and are chemically distinct from water in the regional carbonate aquifer. This difference provides a means of examining vertical transport and groundwater mixing processes. In combination with other geochemical and hydrogeologic data, the end members defined here provide constraints on aquifer residence times and mixing ratios.     

A natural analogue for the long-term corrosion of copper nuclear waste containers—reanalysis of a study of a bronze cannon

The study of natural analogues is often used to support long-term predictions of the safety of geological disposal of used nuclear fuel. The case of a bronze cannon, submerged in seawater-saturated clay sediments for a period of 310 a, is reassessed with reference to a corrosion mechanism developed for copper nuclear waste containers in a conceptual disposal vault in the Canadian Shield. Redox reactions between Cu, Fe and dissolved O₂ are believed to have played an important role in the corrosion of the bronze cannon and also form an essential part of the corrosion mechanism proposed for nuclear waste containers. Limited rates of mass transport through compacted clay are also important in determining the corrosion behaviour of both the cannon and the containers.     

Geochemical exploration in China

Geochemical exploration in China was commenced in the early 1950's. In 1951, the first experimental work was carried out in Yeshan, and a geochemical exploration section was set up in the Ministry of Geology in 1953.Regional geochemical reconnaissance (metallometric surveying) was initiated in 1956 on a nation-wide scale. Soil samples have been collected, and analyzed by semiquantitative spectrography. The results were heavily biased and were not adequately processed and utilized. Renewed efforts have been made to reprocess the vast amount of data accumulated and to utilize them more fully in mineral exploration.Meanwhile, another nation-wide project of regional geochemistry using more refined techniques is in its preparatory stage. It is the Regional Geochemistry-National Reconnaissance Project. In this project stream sediment sampling with a density of one per km² will be used in China Proper, and low-density sampling of various kinds of media in different environments will be used in remote areas. Pilot surveys covering areas of several thousand square kilometers are being undertaken in several provinces.Beside regional reconnaissance, geochemical prospecting has been carried out at virtually all phases of mineral prospecting in China.A brief summary of current research in exploration geochemistry taken by research institutes and universities is given, including studies on the methodology of regional geochemical surveys, primary halos around various types of ore deposits, mercury vapor survey techniques, refinement of analytical methods and instrumentation, and computerized data processing and plotting techniques.Several case histories are described where geochemical exploration techniques have led to successful ore discoveries in China.     

High‐resolution seismic reflection profiling of neotectonic faults in Lake Timiskaming,Timiskaming Graben,Ontario‐Quebec,Canada

The Timiskaming Graben is a 400 km long, 50 km wide north‐west trending morphotectonic depression within the Canadian Shield of eastern North America and experiences frequent intraplate earthquakes. The graben extends along the border of Ontario and Quebec, connecting southward with the Nipissing and Ottawa‐Bonnechere grabens and the St. Lawrence Rift System which includes a similar structure underlying the Hudson Valley of the eastern USA. Together they form a complex failed rift system related to regional extension of North American crust during the breakup of Rodinia and, later, Pangea. The Timiskaming Graben lies within a belt of heightened seismic activity (Western Quebec Seismic Zone) with frequent moderate magnitude (greater than magnitude 5) earthquakes including a magnitude 6.2 in 1935. These events threaten aging urban infrastructure built on soft glacial sediments; post‐glacial landslides along the Ottawa Valley suggest earthquakes as large as magnitude 7. The inner part of the Timiskaming Graben is filled by Lake Timiskaming, a large 110 km long post‐glacial successor to glacial Lake Barlow that was ponded by the Laurentide Ice Sheet 9500 years ago. The effects of frequent ground shaking on lake floor sediments was assessed by collecting more than 1000 line kilometres of high‐resolution ‘chirp’ seismic profiles. Late glacial Lake Barlow glaciolacustrine and overlying post‐glacial sediments are extensively deformed by extensional faults that define prominent horsts and grabens; multibeam bathymetry data suggest that faults influence the morphology of the modern lake floor, despite high sedimentation rates, and indicate recent neotectonic deformation. The Lake Timiskaming area provides evidence of post‐glacial intracratonic faulting related to recurring earthquake activity along a weak spot within the North American plate.     

Effect of source integration on the geochemical fluxes from springs

Geochemical fluxes from watersheds are typically defined using mass-balance methods that essentially lump all weathering processes operative in a watershed into a single flux of solute mass measured in streamflow at the watershed outlet. However, it is important that we understand how weathering processes in different hydrological zones of a watershed (i.e., surface, unsaturated, and saturated zones) contribute to the total geochemical flux from the watershed. This capability will improve understanding of how geochemical fluxes from these different zones may change in response to climate change. Here, the geochemical flux from weathering processes occurring solely in the saturated zone is investigated. This task, however, remains exceedingly difficult due to the sparsity of subsurface sampling points, especially in large, remote, and/or undeveloped watersheds. In such cases, springflow is often assumed to be a proxy for groundwater (defined as water residing in fully saturated geologic formations). However, springflow generation may integrate different sources of water including, but not limited to, groundwater. The authors’ hypothesis is that long-term estimates of geochemical fluxes from groundwater using springflow proxies will be too large due to the integrative nature of springflow generation. Two conceptual models of springflow generation are tested using endmember mixing analyses (EMMA) on observations of spring chemistries and stable isotopic compositions in a large alpine watershed in the San Juan Mountains of southwestern Colorado. In the “total springflow” conceptual model, springflow is assumed to be 100% groundwater. In the “fractional springflow” conceptual model, springflow is assumed to be an integration of different sources of water (e.g., groundwater, unsaturated flow, preferential flow in the soil, etc.) and groundwater is only a fractional component. The results indicate that groundwater contributions in springflow range from 2% to 100% overall and no springs are consistently composed of 100% groundwater; providing support for the fractional springflow conceptual model. Groundwater contributions are not strongly correlated with elevation, spring contributing area, spring discharge, or seasonality. This variability has a profound effect on long-term geochemical fluxes. The geochemical fluxes for total springflow overestimate long-term solute release by 22–48% as compared to fractional springflow. These findings illustrate that springflow generation, like streamflow generation, integrates many different sources of water reflecting solute concentrations obtained along many different geochemical weathering pathways. These data suggest that springs are not always ideal proxies for groundwater. Springs may be integrating very distinct portions of the groundwater flow field and these groundwater contributions may become mixed at the spring emergence with much younger sources of water that have never resided in the groundwater system.