error in bootloader config while system init

[znavko]

Hello! I want to install guix, but have troubles with bootloader configuration. 
I parted my disk this way:

# fdisk -l /dev/sdb

        Disk /dev/sdb: 59.6 GiB, 64023257088 bytes, 125045424 sectors Units: 
sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 
bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: gpt 
Disk identifier: 3E7A5583-EC16-4444-BD05-F488879F5F8 Device Start End Sectors 
Size Type /dev/sdb1 2048 104859647 104857600 50G Linux filesystem /dev/sdb2 
104859648 125045390 20185743 9.6G Linux swap  
# guix system init /mnt/etc/config.scm /mnt 2>err
# cat err | nc termbin.com 9999
https://termbin.com/r3oh

# cat /mnt/etc/config.scm | nc termbin.com 9999
https://termbin.com/r5rq
Please, what is wrong?

        (operating-system (host-name "antelope") (timezone "Europe/Moscow") 
(locale "en_US.utf8") (bootloader (bootloader-configuration (bootloader 
grub-bootloader) (target "/dev/sdb"))) (file-systems (cons (file-system (device 
"/dev/sdb1") (mount-point "/mnt") (type "ext4")) %base-file-systems)) 
(swap-devices '("/dev/sdb2"))