NEW MEXICO
NM/BM/NMGRL/AL
The New Mexico Geochronology Research Laboratory (NMGRL) in Socorro is a state-of-the-art 40Ar/39Ar dating facility administered by the New Mexico Bureau of Mines at the New Mexico Institute of Mining and Technology. 40Ar/39Ar research at NMGRL is directed by Bill McIntosh and Matt Heizler who have over 25 years combined experience in the field of argon geochronology and thermochronology. The lab also employs two full-time technicians, Lisa Peters and Richard Esser, who supervise mineral separation, sample irradiation and analyses and data reduction. Since its christening in the winter of 1992, the NMGRL laboratory has performed over 60,000 single sample analyses. Necessary in this regard is the software developed by Al Deino at the Institute of Human Origins in Berkeley, California which allows for full automation of extraction line and mass spectrometer functions . The software controls all crucial valves which are operated via pneumatic air drivers. Additional automation comes from laser and furnace sample "packages" which can contain up to 221 and 17 individual samples per load, respectively. Once under vacuum, sample analyses do not require the physical presence of laboratory personnel for extended periods of time. Argon gas extraction at NMGRL is accomplished either by resistance furnace or CO2 laser heating. The first method consists of a double vacuum resistance furnace with molybdenum crucible and crucible liner. Temperatures accuracy is ?10?C; precision is ?1?C; maximum temperature is 1750?C. Argon blanks for the entire furnace extraction line (dual stage) are on the order of 5E-16 moles of 40Ar. The addition of a gate valve between the crucible and sample holder in the near future will likely decrease system blank as well as reduce turn around time for sample changes. The second argon extraction method employs a 10 watt CO2 laser. The CO2 laser provides many of the advantages of other lasers used in argon extraction (e.g. Ar-ion and Nd-Yag) but requires only a fraction of the cost to set up. The CO2 laser at NMGRL is used mainly for the total-fusion of sanidine crystals which include J-value determinations from Fish Canyon Tuff (FC-1) sanidine monitors. System blanks for the laser (single stage) are on the order of 2xE-16 moles of 40Ar. Future innovations at NMGRL include the implementation of a cold-finger to trap H2O from hydrous mineral phases. A new laser system with smaller spot-size capabilities will be able to examine within-grain variations in argon distribution. An ion-counter on the mass spectrometer will allow smaller sample sizes to be used without decreasing accuracy or precision. Also, future integration of a Vacscan Quadrupole mass spectrometer will allow pre-screening of potentially harmful gas before it is equilibrated with the mass spectrometer. Website: "https://geoinfo.nmt.edu/labs/argon/home.html" [Summary provided by NMGRL]