It might be possible.
The routing part is easy - if I understand your case right, you simply need your mobile connection to be used only for access to the IP addresses of your intranet and the ADSL connection to be used for the rest, which is easily provided by configuring the mobile connection to add a default route with a high value of distance or not add it at all (depending whether it is a router connected using Ethernet or a 3G/4G modem connected to the Mikrotik), and manually add route(s) to the intranet subnet(s) via that gateway; more precise (longer) prefixes always have precedence over wider (shorter) prefixes, so packets towards the intranet will choose the manually added routes while packets to other destinations will take the default route with lower distance value, i.e. the one via ADSL.
What makes it difficult is the need to use a dedicated DNS for intranet access; Mikrotik is not really good here and you’ll have to follow @Sob’s suggestion how to use /ip firewall layer7-protocol to redirect the DNS packets from your LAN hosts to the Intranet DNS server if the query goes for the intranet domains, and let them use the standard DNS (the Mikrotik itself or any public one depending on your configuration) for the rest.