草酸的稳定性及CO_2包裹体压力计实验研究

Experimental study on the stability of oxalic acid and carbon dioxide manometer

应用金刚石压腔(diamond-anvil cell)实验技术,对草酸的稳定性进行了研究。草酸在高压低温条件下可以稳定存在,而在低压高温条件下将分解为CO2、H2O等气体。当成矿流体遇到破裂带或裂隙而发生减压沸腾时,可以使成矿流体中的有机络合物迅速发生分解产生大量CO2,从而造成金属元素在有利的空间沉淀、富集成矿。同时,实验研究了高温高压条件下CO2的物理化学性质,得到了CO2包裹体压力计的测定方程:P(MPa)=271.517·(Δν1381.93-0.010987·ΔT)+0.1,式中Δν1381.93(cm-1)为待测包裹体中CO2的拉曼位移相对于常温常压下CO2的拉曼位移1381.93cm-1之差,ΔT(℃)为待测包裹体的温度与常温(23℃)之差,P(MPa)为待测包裹体的内压。由上式计算拉曼位移ν的标准偏差为±0.2cm-1,压力P的误差为±54MPa。该压力标定方程适用于在高压下温度范围为23℃≤T≤390℃的压力标定。

In this study,diamond-anvil cell combined with Raman spectroscopy are applied to in situ investigate the stability of oxalic acid. The oxalic acid can preserve stably at low temperature and high pressure,however it will decompose into CO2 and H2O under the conditions of high temperature and low pressure. When the ore-forming fluids encountered the fracture,the organic complexes would be transformed into CO2 quickly both by the elevated temperature and the decrease of pressure. Consequently,the metals will precipitate and concentrate in favorable space. In addition,the physical and chemical properties of carbon dioxide are also studied.The equation for determining the pressure of CO2-rich inclusions by Raman shift of CO2 is P（ MPa） = 271. 517·（ Δν1381. 93- 0. 010987·ΔT） ＋ 0. 1,where Δν1381. 93（ cm- 1） is the Raman shift（ cm- 1） relative to that of the 1381. 93cm- 1line at 0. 1MPa and ambient temperature,ΔTis the temperature relative to 23℃,P（ MPa） is the inner pressure of the inclusion. The standard deviation of Raman shift is ± 0. 2cm- 1and the uncertainty of pressure is ± 54 MPa. This equation is suitable for pressure calibration under high pressure between 23℃ and 390℃.