Interstitial Liquid Research Articles

Infrared detection of liquids on terrestrial surfaces by CO_2 laser heating

The strong mid-infrared bands of contaminant liquids wetting sand and soil can be remotely detected by 0.103-eV laser irradiation with beam intensity well below that which chars the terrain. Emissions from heated nonvolatile interstitial liquid layers and extinction of thermoluminescence by beam-generated vapors of volatile contaminants are spectrally distinct within the infrared contaminant fingerprint spectral region-as measured by a Michelson interferometer based FT-IR radiometer instrument. The contaminant's vibrational resonance intensities change proportionally in magnitude and sign in measured contiguous difference FFT spectra, within a specific beam-to-sample dwell period. The onset irradiation time and period for detecting these bands can differ according to amount and volatility of contaminant, beam intensity and its time of dwell necessary to produce sufficient thermoluminescence flux, and on the quantity of interferogram data acquisitions.

Magmatic inclusions in the Holocene rhyolites of Newberry Volcano, central Oregon

The 1350 years B.P. Big Obsidian Flow (BOF) at Newberry Volcano in central Oregon contains a wide variety of mafic magmatic inclusions. Although little grain size variation is observed within single inclusions, within the suite textures vary continuously from fine‐grained (“quench”) to coarse‐grained (“cumulate”). The BOF inclusion suite, therefore, defies conventional genetic classifications. Detailed petrographic and geochemical observations require a new model for inclusion formation. Only a few of the finer‐grained inclusions have margins suggestive of liquid‐liquid interaction. Interstitial glass content (≈ 20 vol %) and composition (high‐silica rhyolite) are approximately constant throughout the suite. Mineral compositional zoning is greater in the coarse‐grained than fine‐grained inclusions. Whole inclusion compositions vary significantly but do not correlate well with textural diversity. We interpret the BOF inclusion suite to be a heterogeneous sample set of whole inclusions and parts of disaggregated inclusions. The compositional variability of the suite can be explained by a combination of preentrapment (hybridization) and postentrapment (interstitial liquid loss/gain) processes. Preentrapment hybridization involved mixing of basaltic andesite magma similar to Holocene flank flows and up to 30% rhyolitic liquid. The BOF inclusions may demonstrate the recent existence of mafic magma in the Newberry system. Inclusion features characteristic of small ΔT are consistent with the crystal‐free nature of the BOF, suggesting that the rhyolite may have been superheated. If true, a crystal fractionation origin for the BOF rhyolite is unlikely. The disaggregation of grain size and compositionally zoned inclusions, which produced the observed textural diversity in the BOF suite, compounds problems of interpreting mafic inclusions in silicic volcanic rocks and, more so, in plutonic equivalents.

Clearance of lung edema into the pleural space of volume-loaded anesthetized sheep

To determine whether lung edema leaks into the pleural space, we measured flow rates of visceral pleural liquid from exposed sheep lungs during volume loading and then compared the protein concentration of visceral pleural liquid and lung interstitial liquids (lymph and peribronchovascular cuff liquid). For 4 h, we volume loaded 24 anesthetized ventilated sheep with one side, both sides, or neither side of the chest open. During the experiment, we collected visceral pleural liquid from a bag surrounding the exposed lung and lung lymph; after the experiment, we collected peribronchovascular cuff liquid. We found that during volume loading visceral pleural liquid flow increased significantly by 2 h, and its protein concentration over the final hour was the same as that of lung interstitial liquids. The volume of visceral pleural liquid correlated with excess lung water and wedge pressure elevation. By our estimates, clearance of edema from the lung into the pleural space constituted 23-29% of all edema liquid collected, similar to measured lymph edema clearance. We conclude that edema liquid leaks directly from edematous sheep lungs into the pleural space and that this leakage provides an important additional route of edema clearance.

The Influence of Interstitial Liquids on the Cohesive Strength of Carbon-Black Agglomerates

Abstract The influence of interstitial liquids on the cohesive strength of carbon black has been investigated. Calculations of effective Hamaker coefficients for the wet materials predicted order of magnitude decreases from the Hamaker constants for the dry materials. Tensile-strength data showed slight increases over the Hamaker constants for the dry materials. It is clear that further research is needed to elucidate the effects of liquid content and wettability.

Lung expansion and the perialveolar interstitial pressure gradient.

We have determined the combined effects of lung expansion and increased extravascular lung water (EVLW) on the perialveolar interstitial pressure gradient. In the isolated perfused lobe of dog lung, we measured interstitial pressures by micropuncture at alveolar junctions (Pjct) and in adventitia of 30- to 50-microns microvessels (Padv) with stopped blood flow at vascular pressure of 3-5 cmH2O. We induced edema by raising vascular pressures. In nonedematous lobes (n = 6, EVLW = 3.1 +/- 0.3 g/g dry wt) at alveolar pressure of 7 cmH2O, Pjct averaged 0.5 +/- 0.8 (SD) cmH2O and the Pjct-Padv gradient averaged 0.9 +/- 0.5 cmH2O. After increase of alveolar pressure to 23 cmH2O the gradient was abolished in nonedematous lobes, did not change in moderately edematous lobes (n = 9, EVLW = 4.9 +/- 0.6 g/g dry wt), and increased in severely edematous lobes (n = 6, EVLW = 7.6 +/- 1.4 g/g dry wt). Perialveolar interstitial compliance decreased with increase of alveolar pressure. We conclude that increase of lung volume may reduce perialveolar interstitial liquid clearance by abolishing the Pjct-Padv gradient in nonedematous lungs and by compressing interstitial liquid channels in edematous lungs.

Sequence of interstitial liquid accumulation in liquid-inflated sheep lung lobes.

In the initial stages of pulmonary edema, liquid accumulates in the lung interstitium and appears as cuffs around pulmonary vessels. To determine the pattern, rate, and magnitude of cuff formation, we inflated sheep lungs to capacity with liquid (inflation pressure 19 cmH2O) for 3-300 min. After freezing the lobes in liquid N2, we measured perivascular cuff size and total perivascular volume in frozen blocks of each lobe and compared the results with previous measurements in dog lungs. Total cuff volume in sheep lungs reached a maximum value of 5% of air space volume, compared with 9% in dog lungs. In sheep lungs 94% of vessels greater than or equal to 0.5 mm diam and 16% of smaller vessels were surrounded by cuffs. In dog lungs these values were 99 and 47%, respectively. The ratio of cuff area to vessel area reached a maximum of 2.3 in sheep lungs and 3.4 in dog lungs. In an electrical analogue model designed to simulate cuff growth, estimated interstitial resistance to liquid flow was 6-15 times higher than similar estimates in dog lungs. These species differences might be the result of differences in the composition of the interstitial gel or to differences in the mechanical linkage between the lung parenchyma and vessel wall.

Relationship between conductivity of concrete and corrosion of reinforcing bars

AbstractAn attempt is made to explain the roleplayed by the conductivity of concrete in the corrosion of reinforcing bars. Tests carried out on bimetallic couples embedded in concrete support the hypothesis of direct proportionality between concrete conductivity and corrosion rate. Severalfactors rule out the hypothesis of ohmic control. On the contrary, it is suggested that the process of corrosion is governed by the fraction of the metallic surface wetted by the interstitial liquid present in the concrete.

The effects of bubbles on the volume fluxes and the pressure gradients in unsteady and non-uniform flow of liquids

In this paper the motion of a single bubble or particle in an accelerating liquid flow is analysed using a generalized force equation. The motion of the bubble relative to the fluid gives rise to a drift flux of liquid which affects the mean flow field of the liquid. This flux is calculated in terms of the effective or added mass coefficient of the bubble, C m, which is equal to 1 2 for a small bubble at high Reynolds number. By analysis of the flow in terms of the three flow fields associated with the interstitial liquid, the displaced liquid and the bubble itself, we obtain a rational method for calculating the forces acting on the bubble, the mass conservation equations and the pressure field in the liquid. For a bubbly flow with low void fraction this form of the mass conservation equations reduces to an expression for liquid and gas superficial velocity as a function of relative velocity (the slip measured relative to the interstitial velocity, to be defined) and void fraction, where the constants are defined in terms of C m. Unlike the commonly used relation of Zuber & Findlay (1965), our expression can be generalized to non-uniform flows. Our predictions (using C m = 1 2 ) agree with Zuber & Findlays' empirical equations for low void fraction ϵ in a vertical pipe. They do not, however, agree for high values of ϵ. A new analysis of the mean pressure field in disperse two-phase flow is presented. While the bubbles respond to the interstitial velocity and pressure field, the pressure of interest is usually the average over the whole liquid volume. We show how these are related. The models developed here are applied to the practically important flow of air bubbles in an inclined nozzle, and are compared with recent laboratory measurements.

Foam separation of microbial cells

Batch foam separation has been employed to separate Saccharomyces carlsbergensis cells from their broth without the use of any external surface-active agent. A model has been developed to predict the foamate cell concentration as well as the variation of cell concentration in the bulk liquid in the foam column as a function of time. The model assumes a linear equilibrium relation between the cell concentrations at the interface and the bulk. The foam has interface as well as interstitial liquid. The interface is assumed to be in equilibrium with the interstitial liquid, which in turn is assumed to have the same concentration as the bulk. The interfacial area is calculated by assuming the foam bubbles to be pentagonal dodecahedral in shape. The model has been found to explain the results of foam separation of cells quite well, particularly with respect to the effect of bubble size and aeration rate.

Permeability to interbubble gas diffusion in liquid foam

Changes over time in initially sharply bimodal distributions of bubble size in aqueous foam were measured in a more representative manner than heretofore. Results confirm that the permeability to gas transfer between bubbles can exceed that of Fick's law. This supports the importance of micromixing in the interstitial liquid.

Forearm arterial pressure-volume relationships in man.

Pressure-volume (p-V) relationships of a segment of the forearm circulation have been measured in nine male healthy subjects. Forearm volume was measured using electrical impedance plethysmography, arterial transmural pressure by subtracting mean arterial pressure measured contralaterally in a finger from the pressure in a cuff placed over the sensing electrodes of the plethysmograph. A special two-phase measurement waveform was designed with which cuff pressure was first increased step wise to a suprasystolic level and held at that level for 120 s, then ramped down to zero pressure in another 300 s. The step phase inflation allowed us to estimate the parameters of the interstitial liquids and total blood compartments. The total blood compartment amounted to 6.2 ml per 100 ml of tissue. The ramp phase deflation allowed us to discriminate between a first phase in which only the arteries refilled and a second phase in which the veins also distended. An arctangent function was fitted to the first phase arterial p-V relationship, describing it in model form. Total arterial volume per 100 ml of tissue amounted to 3.8 ml at physiological pressures, total arterial compliance of the forearm per centimetre length to 19.5 microliter kPa-1 cm-1 (2.6 microliter mmHg-1 cm-1) at physiological pressures, and to 340 microliter kPa-1 cm-1 (45 microliter mmHg-1 cm-1) maximum compliance at the lower, inflection point pressures. These values are in general agreement with the literature. Pulse wave velocity cannot be computed reliably from these data.

Equivalent pore estimate for the alveolar-airway barrier in isolated dog lung

In high-pressure pulmonary edema, lung interstitial and air space edema liquids have equal protein concentrations (Am. J. Physiol. 231: 1466, 1976). This suggests that the alveolar-airway barrier separating the air and interstitial spaces is relatively unrestrictive, even without apparent epithelial injury. To estimate the equivalent pore population of the alveolar-airway barrier we inflated each of 18 isolated dog lung lobes for 1 h with a solution of colored tracer of uniform radius. Tracer radii ranged from 1.3 to 405 nm. After freezing the lobes in liquid N2, we measured interstitial tracer concentrations in frozen perivascular cuffs or in samples thawed after dissection from frozen cuffs. Relative to the concentrations instilled, interstitial concentrations ranged from 0.34 for the smallest particles (1.3 and 3.5 nm radius) to zero for particles with radii of 405 nm. From the results we designed a pore model of the alveolar-airway barrier to reproduce the concentrations we measured. No single-pore model could be obtained, although a three-pore model fit the data well. The model results predict that pores with radii of 1, 40, and 400 nm would account for 68, 30, and 2% of total liquid flux, respectively. The majority of liquid flux (68%) would occur through passageways smaller than the smallest tracer we used (1.3 nm radius). We believe the alveolar-airway barrier consists not only of tight intercellular junctions that allow passage of only water and electrolytes but also of a smaller number of large leaks that allow passage of particles up to nearly 400 nm in radius.

ROOSEVELT COUNTY 027: A LOW‐SHOCK UREILITE WITH INTERSTITIAL SILICATES AND HIGH NOBLE GAS CONCENTRATIONS

The lightly‐shocked ureilite RC027 was found in Roosevelt County, New Mexico in 1984. In terms of petrography, texture, mineral compositions, bulk chemical composition, and oxygen isotopic composition it is a typical ureilite. It contains ∼75% olivine (Fo 79.4) and 25% pigeonite (mg 81.3, Wo 8.0), with intergranular graphite and (Fe, Ni) metal. It also contains less than 1% of fine‐grained, interstitial silicate material, which had not previously been recognized in any ureilite. This material is an assemblage of low‐Ca pyroxene (Wo 3.5–9, mg 87–93), augite (Wo 24–36, mg 90–98), glass (typically ∼95% SiO2, 4% Al2O3, 0.5% Na2O), and crystalline SiO2. This material has an igneous texture, indicating that it crystallized from an interstitial liquid. Low‐Ca pyroxene compositions indicate that the interstitial liquid was not in equilibrium with core pigeonite and olivine and cannot have been either an evolved intercumulus liquid or a low‐degree partial melt. It may contain a component of shock‐melted olivine and pigeonite, although petrographic evidence indicates that it could not have been an in situ shock melt. One sample of RC027 has a V‐shaped rare earth element pattern, typical of ureilites. Another is depleted in light rare earth elements (LREE), similar to acid‐treated samples of ureilites, which suggests that LREE in ureilites are contained in an inhomogeneously‐distributed phase. RC027 shows the strongest olivine preferred‐orientation yet observed in a ureilite. Its fabric is characteristic of fabrics formed by tabular minerals in a fluid laminar flow regime and is unlike those formed by syntectonic recrystallization and plastic flow.The elemental and isotopic compositions of noble gases in RC027 are typical of previously analyzed ureilites. This result indicates that there is no correlation of noble gas content with degree of shock in ureilites, and thus suggests that the gases were present in the ureilite material before shock. Cosmogenic He and Ne contents indicate cosmic ray exposure ages of 1.7 and 1.9 Myr, respectively. Thus, RC027 is not paired with Kenna (a ureilite also found in Roosevelt County), which has an exposure age of ∼33 Myr.

Origin and evolution of the ureilite parent magmas: Multi-stage igneous activity on a large parent body

Analyses of olivine and pigeonite cores (interpreted as cumulate crystals) in eight low-shock ureilites show well-defined correlations between Fe/ X (where X is one of the minor elements Mn, Cr, Ca, Al, Ti, P, or Ni) and Fe/ Mg ratios. For the lithophile minor elements these trends are linear, with positive slope, and pass through or near the origin, indicating various degrees of FeO reduction of the parent magmas. The trends shown by P and Ni are consistent with this interpretation, and, additionally, require equilibrium crystallization of 20–27 mole % metal. Graphite was most likely the reducing agent, which implies that the ureilites equilibrated at different pressures, because the graphite fO 2 buffer is pressure dependent. There is no evidence for fractionation of olivine or pryroxene in any of these trends. The Ca, Ti and Al trends show significant scatter, indicating that there must have been multiple parent magmas, with very similar Mg/Mn and Mg Cr ratios, but different Mg Al , Mg Ca and Mg Ti ratios. CaO/Al 2O 3 ratios vary by a factor of ~3 among the eight magmas, and are superchondritic (~ 14–32, molar), similar to lunar mare basalts. We propose the following model for generation and crystallization of ureilite parent magmas (UPM). Chondritic material undergoes 10–25% partial melting, leaving a plagioclase-depleted residue. The magma or magmas form a differentiated crust on the ureilite parent body (UPB), with mafic cumulates and plagioclase cumulates spatially separated. Later remelting (<10%) of the mafic cumulates produced the UPM. Siderophile elements indicate that the source region of the UPM had not experienced segregation of metal such as would occur during core formation. In the source region, the pressure must have been at least 0.5–1 kb, because only at pressures this high does the graphite buffer allow iron oxide to be the stable phase relative to metallic iron. The graphite-bearing UPM were emplaced at various levels in the crust, where they were reduced to various extents, dependent on depth. Ureilites are early olivine-pigeonite cumulates from these magmas. Compositions of interstitial, low-Ca pyroxenes indicate that the trapped interstitial liquids from which they crystallized had lower Mn Mg , Cr Mg , Ca Mg , Al Mg and Na Mg ratios than the UPM, and indicate an abrupt change in liquid composition coincident with impact excavation of ureilites. This interstitial material may be derived by mixing a shock melt of nearby olivine-pigeonite cumulates with residual primary liquid. Our model predicts that the UPB had a differentiated crust, did not have a core, and was at least 235 km in radius. The lack of a ureilite-like body among spectrally analyzed asteroids suggests that either the spectral signature of the UPB is not that of ureilites themselves (perhaps of carbon-free feldspathic material instead), that the UPB is not intact, or that ureilites did not originate in the asteroid belt.

Magmatic and metamorphic controls on chemical variations within the Eiksunddal eclogite complex, Sunnmøre, western Norway

The Eiksunddal eclogite complex is one of the larger group B (“country-rock”) eclogites within the Western Gneiss Region (WGR) of Norway. Whole-rock chemical data suggest a magmatic origin for the rocks within the eclogite complex. The chemical variations among the eclogitic rocks were controlled by accumulation of olivine (Fo 80) and plagioclase (An 70) and probably magnetite. The composition of the interstitial (“trapped”) liquid is derived by linear regression methods and is a high-Al orthopyroxene normative basalt. The most likely conditions of crystallization are: T ≈ 1150°C, P < 10 kbar. The Al-rich nature of the interstitial liquid may have implications for the formation of anorthosites and leucogabbros associated with similar mafic rocks elsewhere in the WGR. Trace-element characteristics are compatible with a continental origin of these rocks. During the subsequent metamorphic history, the marginal parts of the complex have suffered variable degrees of contamination. Abundant amphibole inclusions in large garnets in garnet websterites suggest local hydration at pre-eclogitic stages. This may be associated with introduction of radiogenic Sr as previously reported by W.L. Griffin and H.K. Brueckner. During prograde metamorphism, alkali exchange occurred during growth of garnet, clinopyroxene and biotite at the expense of pargasitic amphibole and orthopyroxene. The most extensive metasomatism however, was probably associated with the introduction of fluid during amphibolitization (retrogression) of the eclogitic rocks. Three model reactions — eqs. 5–7 — qualitatively explain the relation between degree of retrogression and the observed metasomatic effects. Whether Si and Ca are gained or lost during retrogression seems to be controlled by the extent of amphibole growth in diopside + plagioclase symplectites initially formed by breakdown of omphacite. Alumina has behaved in a more or less immobile way during metasomatism. Low mobility of Al is also reflected by the formation of subsilic (Al-rich) amphiboles and Al-rich plagioclase during garnet breakdown. This demonstrates the importance of kinetic factors in controlling mineral chemistry.

Crystallisation of nepheline syenite in a subvolcanic magma system: Tenerife, canary islands

The late Quaternary phonolitic pumice deposits of Tenerife, Canary Islands, are the product of a periodically-tapped, periodically-replenished, zoned alkaline magma system. Nepheline syenite blocks occur as lithics in the deposits, and provide solidified representatives of the phonolite magmas. The blocks are considered to have crystallised in the roof zone of the active magma system at a depth of roughly 4 km beneath the Las Cañadas caldera. Conversion of highly-differentiated phonolitic magma to solid nepheline syenite was achieved between 770° and 680°C. Quenched glass of extreme composition in one erupted block provides a sample of the last interstitial liquid; comparison of this sample with phonolitic pumice, and with fully crystallised syenites, allows reconstruction of the magmatic, interstitial and subsolidus crystallisation histories of nepheline syenite. Phases represented by the phenocryst assemblage of the most differentiated phonolitic pumices (sanidine, sodalite, nepheline, Na-poor pyroxene, biotite, sphene and magnetite) formed an initial crystal “mush”, containing abundant trapped liquid, on the walls of the magma chamber. Interstitial crystallisation, involving the conversion of pyroxene to Na-rich compositions, continued growth of felsic phases, and partial to complete consumption of biotite, sphene, magnetite and apatite, was accompanied by extreme sodium enrichment in the residual liquid. Stellate aegirine, lavenite, loparite and Mn-rich ilmenite are among the final products of magmatic crystallisation. Modification of feldspar primocrysts persisted into subsolidus conditions. It is suggested that complete solidification of an open-system alkaline magma chamber results in the formation of an alkaline alkaline ring complex.

Lung liquid and protein exchange: the four inhomogeneities.

William of Ockham, 14th-century scholastic philosopher at Oxford and Munich, emphasized the principle of economy, "pleurality is not to be supposed without necessity" (Ockham's razor). Necessity is the key word. In the modeling of steady-state lung liquid and protein exchange, the desire for simplicity has sometimes outweighed good judgment. In fact, we and others have shown that simple models do not work. It is necessary to include several forms of inhomogeneity. The air-filled lung shows regional (top to bottom) variations of mass, microvascular pressure, and perimicrovascular protein concentration. Normally, the small longitudinal (arterioles to venules) gradient of microvascular and perimicrovascular pressures is not a major concern, but in nonuniform disease processes, such as microembolism, longitudinal inhomogeneity, and parallel inhomogeneity are dominant. Multiple pores should also be considered a form of inhomogeneity. The effect on liquid and protein exchange, when plasma protein concentration or microvascular pressure change, can be readily explained using pore heterogeneity. The model I am currently using consists of a large number of discrete compartments (18), rather than a continuous distribution. We have recently identified a fifth inhomogeneity, which is that lung lymph flow might not always represent steady-state transvascular filtration because interstitial liquid may leak through the pleura or along the bronchovascular liquid cuffs into the mediastinum.

Parenteral nutrition via the peritoneum with dextrose and amino acids.

We filled the peritoneal cavity of 9 rabbits through a silastic pediatric Tenckhoff-type catheter with a volume 10% of the animal's weight of an isotonic 'absorption mass' made up by a hydroelectrolytic solution to which 535 mg/dl glucose and 2.53 g/l L-amino acids were added. Then we slowly and continuously infused into it a mixture of a 50% glucose solution with a 13.3% L-amino acid solution to provide 10 +/- 0.2 g glucose and 2.18 +/- 0.24 g L-amino acid (0.334 +/- 0.039 g nitrogen) per kilogram weight in 24 h. So we mimicked the scheme and quantities of total parenteral nutrition. Osmolarity and volume of peritoneal fluid were constant throughout the experiment. In the first 4 h, glucose concentration rose to 1,407 +/- 431 mg/dl and amino acids decreased to nearly two thirds of their initial concentrations. Thereafter, both amino acid and glucose concentrations stabilized. Blood sugar rose slightly from basal 145 +/- 16 mg/dl to a maximum of 200 +/- 59 mg/dl. Plasma amino acids showed a moderate but irregular variation with increases in proline, glutamic acid, methionine, lysine and arginine concentrations, a decline of isoleucine and tryptophan concentrations and no changes for the other amino acids given. There were no variations in plasma values of sodium, potassium, chloride, urea, creatinine, osmolarity, total proteins and hematocrit. We achieved a glucose absorption of 8.72 +/- 0.94 g/kg weight (87.07 +/- 10.11% of the administered amount) and a nitrogen absorption of 303 +/- 47 mg/kg/day (91.4 +/- 14% of administered amount).(ABSTRACT TRUNCATED AT 250 WORDS)

Compaction of Igneous Cumulates

When initially deposited, mafic igneous cumulates consist of a solid matrix of mineral phases plus 50-60% interstitial liquid. Due to its greater density the matrix compacts, squeezing the interstitial liquid upward. A numerical fluid mechanical model of this process indicates that if the cumulate deposition rate is constant, compaction occurs in one of two distinct models. For rapid deposition, the system is permeability controlled with compaction occurring only at the base of the cumulate pile. For slowly deposited cumulates an additional compaction zone that is partially viscosity-controlled develops at the top of the pile. If the extent of compaction and thickness of this zone are known for a real system, the model can be used to estimate the permeability and effective viscosity of the compacting cumulates. Such calculations yield a permeability of $$1.5 \times 10^{-3}a^{2}f^{3}/(1 - f)^{2}$$ for olivine cumulates in the Muskox Intrusion. Reliable viscosity estimates await an empirical law relating ma...

The role of contamination in the evolution of the Platreef of the Bushveld Complex

The Platreef is a thick (greater than 100 m) coarse-grained feldspathic orthopyroxenite which transgresses northward across metasediments of the Transvaal Sequence and onto a granitic floor. It is overlain by main zone gabbronorites. Vertical profiles for Rb and Sr isotope ratios through the Platreef and overlying main zone show differences depending upon footwall type. Against a granitic floor the Platreef has initial 87 Sr/ 86 Sr ratios ranging from 0.7107 to 0.7226 (calculated at 2.05 b.y.) suggesting heterogeneous contamination by a melt derived from the granite. Overlying a dolomitic footwall, the Platreef shows lower initial ratios (0.7054 to 0.7147), but high Rb contents again suggest addition of a granitic component. The extent of contamination is least at the base. The role of dolomite assimilation is difficult to quantify. The lowermost rocks of the main zone show high Rb contents, due to contamination, but their initial Sr isotope ratios have not been changed significantly, due to the high proportion of cumulus plagioclase. Orthopyroxene has a much lower initial ratio than its whole rock, indicating that the main cumulus phase formed prior to contamination and that the granitic liquid reacted with the interstitial basic magma to produce the contaminated intercumulus phases.The tenor of platinum-group elements in the Platreef precludes the formation of immiscible sulfide liquid from an interstitial liquid; rather, it must be an early formed phase. Hence the separation of sulfide liquid may predate the main siliceous contamination process.