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Context. Determining the metallicities and ages of M31 clusters isfundamental to the study of the formation and evolution of M31 itself. TheLarge Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) has carriedout a systematic spectroscopic campaign of clusters and candidates in M31.Aims. We constructed a catalogue of 346 M31 clusters observed by LAMOST. Bycombining the information of the LAMOST spectra and the multi-band photometry,we developed a new algorithm to estimate the metallicities and ages of theseclusters. Methods. We distinguish young clusters from old using random forestclassifiers based on a empirical training data set selected from theliterature. Ages of young clusters are derived from the spectral energydistribution (SED) fits of their multi-band photometric measurements. Theirmetallicities are estimated by fitting their observed spectral principalcomponents extracted from the LAMOST spectra with those from the youngmetal-rich single stellar population (SSP) models. For old clusters, we builtnon-parameter random forest models between the spectral principal componentsand/or multi-band colours and the parameters of the clusters based on atraining data set constructed from the SSP models. The ages and metallicitiesof the old clusters are then estimated by fitting their observed spectralprincipal components extracted from the LAMOST spectra and multi-band coloursfrom the photometric measurements with the resultant random forest models.Results. We derived parameters of 53 young and 293 old clusters in ourcatalogue. Our resultant parameters are in good agreement with those from theliterature. The ages of about 30 catalogued clusters and metallicities of about40 sources are derived for the first time.

Estimating ages and metallicities of M31 star clusters from LAMOST DR6