Mineralogy, geochemistry, metamorphism, and provenance of the early Proterozoic metamorphic rocks of the central Front Range, Colorado

Gable, Dolores J.

doi:10.3133/ofr96522

Cited by 7 publications

(6 citation statements)

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“…Feldspars are a major mineral phase in the biotite gneiss bedrock. Their composition varies between plagioclase and alkali feldspar [ Gable , ]. In this study, feldspar grains were analyzed and identified as microcline by XRD and had a Ge/Si of 1.88 µmol/mol (Table ).…”

Section: Resultsmentioning

confidence: 99%

“…Differences in moisture retention caused by insolation may explain the presence of a deeper weathering front in the north facing slope [ Befus et al ., ]. The major mineralogical phases in bedrock include plagioclase, potassium feldspar, quartz, and biotite [ Gable , ]. Soils are alfisols with a Bt horizon of accumulated clay or Bw horizon of oxidized saprolite depending on slope aspect [ Birkeland et al ., ; Dethier et al ., ].…”

Section: Site Descriptionmentioning

confidence: 99%

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Colloidal transport in the Gordon Gulch catchment of the Boulder Creek CZO and its effect on C‐Q relationships for silicon

Aguirre

Derry

Mills

et al. 2017

Water Resources Research

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The near‐constant Si concentration under varying discharge observed in Gordon Gulch of the Boulder Critical Zone Observatory (CZO) indicates that the silica fluxes are strongly controlled by discharge. To identify the mechanisms supplying increased Si at high discharge (Q), we examine Si‐Al‐Fe‐Ge in soils, streams, and groundwaters. We identify bedrock weathering in groundwater and colloidal transport as the two end‐members that supply Si to the system. During base flow, streamflow is derived from groundwater, and weathering of feldspar is the main source of Si with a Ge/Si ratio 0.2–0.5 µmol/mol and low dissolved Al and Fe. The groundwater data are consistent with incongruent weathering of feldspar as the main source of dissolved Si. As discharge increases, Si‐Al‐Fe‐bearing colloids are mobilized and the Ge/Si ratio of the stream rises to 3.0 µmol/mol. Mineralogical analysis using XRD identified Al‐Si phases including kaolinite, illite, and quartz in the colloidal size fraction (<0.45 µm). The Ge/Si ratio of stream and soil colloids is ≈3.8 µmol/mol. The mechanism of colloidal transport with increasing discharge can account for the concentration‐discharge (C‐Q) patterns of Si, Al, and Fe with near‐zero or positive power law slopes observed in the Gordon Gulch catchment. Anomalously high Ge/Si ratios also identified a third end‐member resulting from coal fly ash deposition during the winter and spring. Wind trajectories during 2012, correlation between Ge/Si and SO42−, and comparison to atmospheric deposition data imply contamination from nearby coal fired power plant operations.

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Section: Resultsmentioning

confidence: 99%

Section: Site Descriptionmentioning

confidence: 99%

Colloidal transport in the Gordon Gulch catchment of the Boulder Creek CZO and its effect on C‐Q relationships for silicon

Aguirre

Derry

Mills

et al. 2017

Water Resources Research

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“…There are no residential developments in the watershed, but some dirt roads are present near the top of the basin. The watershed primarily is underlain by Precambrian biotite gneiss (Gable, 1996) and has developed a weathered profile 8 to 30 m thick (Befus et al, 2011). Soils are predominantly Alfisols on north‐facing slopes and Mollisols on south‐facing slopes (Dethier et al, 2012).…”

Section: Methodsmentioning

confidence: 99%

Colloid Mobilization and Seasonal Variability in a Semiarid Headwater Stream

et al. 2017

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Colloids can be important vectors for the transport of contaminants in the environment, but little is known about colloid mobilization at the watershed scale. We present colloid concentration, composition, and flux data over a large range of hydrologic conditions from a small watershed (Gordon Gulch) in the foothills of the Colorado Front Range. Colloids, consisting predominantly of Si, Fe, and Al, were present in most stream samples but were not detected in groundwater samples. Mineralogical and morphological analysis indicated that the colloids were composed of kaolinite and illite clays with lesser amounts of amorphous Fe-hydroxides. Although colloid composition remained relatively constant over the sampled flow conditions, colloid concentrations varied considerably and increased as ionic strength of stream water decreased. The highest concentrations occurred during precipitation events after extended dry periods. These observations are consistent with laboratory studies that have shown colloids can be mobilized by decreases in pore-water ionic strength, which likely occurs during precipitation events. Colloidal particles constituted 30 to 35% of the Si mass flux and 93 to 97% of the Fe and Al mass fluxes in the <0.45-µm fraction in the stream. Colloids are therefore a significant and often overlooked component of mass fluxes whose temporal variations may yield insight into hydrologic flowpaths in this semiarid catchment.

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“…The bedrock underlying Gordon Gulch is Precambrian biotite gneiss, with minor granodiorite intrusions (Gable, 1996). Four hydrogeologic units are recognized in Gordon Gulch: soil, saprolite, weathered bedrock, and fresh bedrock (Figure 2 ).…”

Section: Geologymentioning

confidence: 99%

The Role of Groundwater Flow in a Montane, Semi-Arid, Headwater Catchment

Salberg

Anderson

2022

Preprint

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Groundwater is critical in sustaining streamflow, especially in headwater catchments, because of its ability to supply baseflow. In water-limited arid and semi-arid mountain environments, the need to characterize groundwater recharge and discharge has grown in tandem with demands to manage current and future water resources. However, studying groundwater in complex terrain is challenging due to limited field measurements. Nearly a decade of monitoring in Gordon Gulch in the Colorado Front Range provides an opportunity to study such an environment. The field data is used to parameterize and calibrate a groundwater flow model (MODFLOW-NWT). Model results reveal that groundwater is recharged primarily during one to two recharge periods each year, driven by spring snowmelt coupled with rain or by intense/prolonged summer rain. Gordon Gulch is a net gaining stream, with greater fluxes from groundwater to stream in lower Gordon Gulch and during springtime. Groundwater is discharged to the stream via long, deep flowpaths sourced from upper Gordon Gulch and from hillslopes, and via short, shallow flowpaths in lower Gordon Gulch. Modelled groundwater accounts for approximately 16 to 34% of baseflow in the stream. Using Gordon Gulch as a case study, this model and data analysis contribute to a larger effort to understand and constrain the mechanisms driving groundwater recharge and groundwater-stream exchanges in semi-arid, headwater catchments.

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Mineralogy, geochemistry, metamorphism, and provenance of the early Proterozoic metamorphic rocks of the central Front Range, Colorado

Cited by 7 publications

References 0 publications

Colloidal transport in the Gordon Gulch catchment of the Boulder Creek CZO and its effect on C‐Q relationships for silicon

Colloidal transport in the Gordon Gulch catchment of the Boulder Creek CZO and its effect on C‐Q relationships for silicon

Colloid Mobilization and Seasonal Variability in a Semiarid Headwater Stream

The Role of Groundwater Flow in a Montane, Semi-Arid, Headwater Catchment

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