In the last decade, several studies have reported enrichments of the heavy isotopes of moderately volatile elements in lunar mare basalts. However, the mechanisms controlling the isotope fractionation are still debated and may differ for elements with variable geochemical behaviour. Here, we present a new comprehensive dataset of mass-dependent copper isotope compositions (delta 65Cu) of 30 mare basalts sampled during the Apollo missions. The new delta 65Cu data range from +0.14 %o to +1.28 %o (with the exception of two samples at 0.01 %o and -1.42 %o), significantly heavier than chondrites and the bulk silicate Earth. A comparison with mass fractions of major and trace elements and thermodynamic constraints reveals that Cu isotopic variations within different mare basalt suites are mostly unrelated to fractional crystallisation of silicates or oxides and late-stage magmatic degassing. Instead, we propose that the delta 65Cu average of each suite is representative of the composition of its respective mantle source. The observed differences across geographically and temporally distinct mare basalt suites, suggest that this variation relates to large-scale processes that formed isotopically distinct mantle sources. Based on a Cu isotope fractionation model during metal melt saturation in crystal mush zones of the lunar magma ocean, we propose that distinct delta 65Cu compositions and Cu abundances of mare basalt mantle sources reflect local metal melt-silicate melt equilibration and trapping of metal in mantle cumulates during lunar magma ocean solidification. Differences in delta 65Cu and mass fractions and ratios of siderophile elements between low- and high-Ti mare basalt sources reflect the evolving compositions of both metal and silicate melt during the late cooling stages of the lunar magma ocean.

The abundances and isotopic signatures of volatile elements provide critical information for understanding the delivery of water and other essential life-giving compounds to planets. It has been demonstrated that the Moon is depleted in moderately volatile elements (MVE), such as Zn, Cl, S, K and Rb, relative to the Earth. The isotopic compositions of these MVE in lunar rocks suggest loss of volatile elements during the formation of the Moon, as well as their modification during later differentiation and impact processes. Due to its moderately volatile and strongly chalcophile behaviour, copper (Cu) provides a distinct record of planetary accretion and differentiation processes relative to Cl, Rb, Zn or K. Here we present Cu isotopic compositions of Apollo 11, 12, 14 and 15 mare basalts and lunar basaltic meteorites, which range from delta 65Cu of +0.55 +/- 0.01 %o to +3.94 +/- 0.04 %o (per mil deviation of the 65Cu/63Cu from the NIST SRM 976 standard), independent of mare basalt Ti content. The delta 65Cu values of the basalts are negatively correlated with their Cu contents, which is interpreted as evidence for volatile loss upon mare basalt emplacement, plausibly related to the presence Cl- and S-bearing ligands in the vapour phase. This relationship can be used to determine the Cu isotopic composition of the lunar mantle to a delta 65Cu of +0.57 +/- 0.15 %o. The bulk silicate Moon (BSM) is 0.5%o heavier than the bulk silicate Earth (+0.07 +/- 0.10 %o) or chondritic materials (from -1.45 +/- 0.08 %o to 0.07 +/- 0.06 %o). Owing to the ineffectiveness of sulfide segregation and lunar core formation in inducing Cu isotopic fractionation, the isotopic difference between the Moon and the Earth is attributed to volatile loss during the Moon-forming event, which must have occurred at- or nearequilibrium.

Copper, a malleable and ductile transition metal, possesses two stable isotopes. These copper isotopic composition data have recently found diverse applications in various fields and disciplines. In geology, copper isotopes serve as tracers that aid in investigating ore formation processes and the mechanisms of copper deposits Likewise, it has emerged as a valuable tracer in polluted environments. In plant biology, copper acts as an essential micronutrient crucial for photosynthesis, respiration, and growth. Copper isotopes contribute to understanding how plants uptake and dispense copper from the soil within their tissues. Similarly, in animals, copper serves as an essential trace element, playing a vital role in growth, white blood cell function, and enzyme activity. In humans, copper acts as an antioxidant, neutralising harmful free radicals within the body. It also helps in maintaining the nervous and immune system. Furthermore, copper isotopes find medical applications, particularly in cancer diagnostics, neurodegenerative diseases, and targeted radiotherapy. However, excessive copper can have detrimental effects in humans such as it can cause liver damage, nausea, and abdominal pain, whilst in plants it can affect the growth of plants, photosynthesis, and membrane permeability. This review emphasises the significance of copper and its isotopes in geology, the environment, and human health.

The Apollo 16 'Rusty Rock' impact melt breccia 66095 is a volatile-rich sample, with the volatiles inherited through vapor condensation from an internal lunar source formed during thermo-magmatic evolution of the Moon. We report Cu and Fe isotope data for 66095 and find that bulk-rocks, residues and acid leaches span a relatively limited range of compositions (3.0 +/- 1.3 wt.% FeO [range = 2.0-4.8 wt.%], 5.4 +/- 3.1 ppm Cu [range = 3-12 ppm], average delta Fe-56 of 0.15 +/- 0.05 parts per thousand [weighted mean = 0.156 parts per thousand] and delta Cu-65 of 0.72 +/- 0.14 parts per thousand[weighted mean = 0.78 parts per thousand]). In contrast to the extreme enrichment of the light isotopes of Zn and heavy isotopes of Cl in 66095, delta Fe-56 and delta Fe-56 in the sample lie within the previously reported range for lunar mare basalts (0.92 +/- 0.16 parts per thousand and 0.12 +/- 0.02 parts per thousand, respectively). The lack of extreme isotopic fractionation for Cu and Fe isotopes reflects compositions inherent to 66095, with condensation of a cooling gas from impact-generated fumarolic activity at temperatures too low to lead to the condensation of Cu and Fe in the sample, but higher than required to condense Zn. Together with thermodynamic models, these constraints suggest that the gas condensed within 66095 between 700 and 900 degrees C (assuming a pressure of 10(-6) and an fO(2) of IW-2). That the Cu and Fe isotopic compositions of sample 66095 are within the range of mare basalts removes the need for an exotic, volatile-enriched source. The enrichment in Tl, Br, Cd, Sn, Zn, Pb, Rb, Cs, Ga, B, Cl, Li relative to Bi, Se, Te, Ge, Cu, Ag, Sb, Mn, P, Cr and Fe in the 'Rusty Rock' is consistent with volcanic outgassing models and indicates that 66095 likely formed distal from the original source of the gas. The volatile-rich character of 66095 is consistent with impact-generated fumarolic activity in the region of the Cayley Plains, demonstrating that volatile-rich rocks can occur on the lunar surface from outgassing of a volatile-poor lunar interior. The 'Rusty Rock' indicates that the lunar interior is significantly depleted in volatile elements and compounds and that volatile-rich surface rocks likely formed through vapor condensation. Remote sensing studies have detected volatiles on the lunar surface, attributing them dominantly to solar wind. Based on the 'Rusty Rock', some of these surface volatiles may also originate from the Moon's interior. (C) 2019 Elsevier Ltd. All rights reserved.