Context : A previous study of F and G main-sequence stars in the solar neighborhood has revealed the existence of two distinct halo populations with a clear separation in [ \alpha /Fe ] for the metallicity range -1.4 < [ Fe/H ] < -0.7 .
Taking into account the kinematics and ages of the stars , some Galactic formation models suggest that the ‘ high-alpha ’ halo stars were formed in situ , whereas the ‘ low-alpha ’ stars have been accreted from satellite galaxies .

Aims : In this paper we investigate if there is a systematic difference in the lithium abundances of stars belonging to the high- and low-alpha halo populations .

Methods : Equivalent widths of the Li i 6707.8 Å resonance line are measured from high resolution VLT/UVES and NOT/FIES spectra and used to derive Li abundances on the basis of MARCS model atmospheres .
Furthermore , masses of the stars are determined from the log T _ { eff } – log g diagram by interpolating between evolutionary tracks based on Yonsei-Yale models .

Results : There is no significant systematic difference in the lithium abundances of high- and low-alpha stars .
For the large majority of stars with masses 0.7 < M / M _ { \odot } < 0.9 and heavy-element mass fractions 0.001 \la Z < 0.006 , the lithium abundance is well fitted by a relation A ( Li ) = a _ { 0 } + a _ { 1 } M + a _ { 2 } Z + a _ { 3 } M Z , where a _ { 0 } , a _ { 1 } , a _ { 2 } , and a _ { 3 } are constants .
Extrapolating this relation to Z = 0 leads to a lithium abundance close to the primordial value predicted from standard Big Bang nucleosynthesis calculations and the WMAP baryon density .
The relation , however , does not apply to stars with metallicities below \mbox { [ Fe / H ] } \simeq - 1.5 .

Conclusions : We suggest that metal-rich halo stars were formed with a lithium abundance close to the primordial value , and that lithium in their atmospheres has been depleted in time with an approximately linear dependence on stellar mass and Z .
The lack of a systematic difference in the Li abundances of high- and low-alpha stars indicates that an environmental effect is not important for the destruction of lithium .